I am no "Copyright lawyer" or can I say have studied more than a general skim through the Australian Copyright Act, so the following is my understanding of why respect for obtaining Copyright Permission is important.
Indeed Copyright Laws can be different in different countries, but the following is hopefully generic enough to provide some relevant introduction.

Why should we bother?

You are probably reading this because of one of my replies to a LinkedIn post about a potential breach of Copyright, or at least whether permission has been obtained from the Copyright holder for that document to have been posted on LinkedIn. 

Some times, some may object and even argue with me about whether the referenced post is a breach of Copyright, or even try to tell me, even abuse me, that I am being pedantic and/or over-zealous.

I (try to) wear with pride my professional ethics and respect for the Copyright holders and all that Copyright entitles them to.
I (try to) wear with pride my efforts to advise and/or encourage and/or "call out" about Copyright issues.

It is the abuse of Copyright and "licence to use" Copyright material by some that I see all too often that is the reason I do not provide "electronic copies" of any of the training courses I run. 
Even writing a book (as I often consider doing) is something I generally shy away from due to the potential loss of income due to breach of the Copyright (yes, I know the irony/conundrum/conflict of no income versus potential reduced income 🤦‍♂️😞🤔). My friends often say I give away too much for free in this technical reference site and LinkedIn, so you may be able to imagine the information I provide in my fee-based courses.

So let me save some of the argument and abuse and state my views about Copyright, and expectations about how professionals should demonstrate their professionalism in respecting Copyright.

Please note though that this page, and others here, is itself protected by Copyright. 

However you can distribute as you wish the following link as a permanent link (i.e. don't use the direct URL in the browser address bar as that is volatile):
https://ideology.atlassian.net/l/c/oHZ7imbx    or    https://tinyurl.com/4zktmrpn 

Basis of Copyright 

Copyright gives the holder EXCLUSIVE RIGHT to decide when, how and where a document is distributed. 
I know it is "only Wikipedia", but it is where most of us would start https://en.wikipedia.org/wiki/Copyright

Copyright is automatic (i.e. regardless of whether a © symbol is used or not) when the document is created and (depending on the duration stipulated by national Laws) remains for 50-100 years after the Copyright holder dies or ceases to exist as an entity.
So inherently that means for that time after death there is no one to give permission for redistribution, so it must not be redistributed by anyone in that time frame.

The underlying principle of Copyright, and Patents, is balancing and protecting the ability for the copyright/patent owner to monetize their idea if they so choose against the benefits (free-of-charge or fee-based) to society for distributing that idea as needs be .

A copyright holder can make the material available to whomever however they wish to do so, and as payment-based or at no charge.

The fact that it has been made available does not provide an licence or permission for others to redistribute that material in any manner they so choose without first obtaining permission from the copyright holder.

Why is respect for Copyright Permission important?

In some cases the Copyright holder expects to obtain financial return from the distribution of the document with it being sold in some form to the readers.

As examples,

• Standards are “in the public domain” but are sitting behind a paywall.
  
  
• Text books (physical or electronic copies) are written by authors with the direct expectation that will get paid income for each copy, and in fact the Copyright holder is often the publishing house.
  
  
• CIGRE Technical Brochures and Green Books are Copyright and only accessed via the e-cigre paywall https://e-cigre.org/, even though Individual Members and staff of Collective Members (according to the  number of accounts within a Collective Member rule) can download for free.
  
  
• In other cases it may be a technical paper or report or even a set of slides from a presentation of some form, perhaps at a Conference.

Copyright for deciding how it is further distributed remains with the author(s)!

There is no "excuse" for breaching Copyright based on how the document was created e.g. volunteer effort for writing a Standard or a CIGRE Technical Brochure or Green Book. The organisation that provided the context and framework for the creation of the document holds the Copyright and it must be respected.

What does Copyright allow others to do?

Copyright applies whether a © symbol is displayed or not.

In some cases, e.g. a product supplier, the Copyright holder may not be overly concerned to the extent of retraining or penalty action about redistribution of their document as it may serve their commercial interests as indirect marketing and promotional activity.
However it cannot be assumed that a supplier is not concerned and/or the document considered as not requiring their permission.

The Copyright holder may provide some overall “licence” and/or restriction for how that document can be used, copied in whole or part, stored or redistributed.

The document may be restricted in various ways that, as examples of the types of restrictions/licence that you might find, it:

• “must not be copied in whole”
• “must not be copied in whole or in part” which means you cannot copy even a single diagram, image, table or sections of text.
• “must only be stored for personal access on your computer”, which means it must not be stored on the company server for anyone else in the company to access
• .. and others

… and any of those may have some form of additional caveat “unless permission has been granted”.  
This means you need to ask the Copyright holder and receive their written permission – if that is successful it probably is a good idea to least that your subsequent use of it states in some way “with Permission”

On the other hand the caveat may give some open licence such as:

• “may be copied in small parts with acknowledgement of the source” i.e. you can copy bits and pieces provided the Copyright holder is cited as the source

Getting approval

In some cases, the Copyright holder anticipates that there will be circumstances and occasions where granting use of their material will be appropriate and/or useful to their own objectives and hence provide a simple and direct means of requesting permission. It is reasonably common for the Copyright holder to provide contact details for requesting permissions, and/or reporting potential breaches.

As an example, official Standards are not allowed to be redistributed beyond the licence arrangement at the time of purchase. 
However, the Standards are often referenced and extracts (e.g. a table/diagram/image/text) of the Standards used in other documents as means of communicating the requirements for complying to the requirements of the Standard, and hence these organisations provide an online request mechanism:

• IEC Standards: https://www.iec.ch/copyright 
• IEEE Standards: https://standards.ieee.org/ipr/stdspermission.html

.. but it is in the "public domain"

“Public domain” is often misunderstood and mis-applied. 

"Public domain" and "public accessible" are two very different issues in Copyright.

"Public domain" only refers to any time AFTER the expiration of the Copyright, i.e. AFTER the 50-100 year exclusive rights period has expired due to death, or cessation of existence of the entity.

Just because a document is on a web site does not put it in the “public domain” and certainly does not even suggest any degree of open licence or authority or permission for someone else to redistribute that document for example by email or by posting on LinkedIn, Facebook or any other web platform.

A document on a "public accessible" web site, or even behind a paywall, STILL has the rules of Copyright applying to it.

This web site and all the pages you can visit ARE "public accessible" (you can GOOGLE them, and distribute links), but they are NOT "in the public domain" because

1. I am still alive (at least as I write this) ,
   or
2. it is less than 70 years after my death.

.. but isn't "fair use" or "fair dealing" allowed?

Clearly the basis of Copyright itself makes no distinction about how others are going to want to use the material.

Indeed the term "fair use" could be very subjective and needs full definition in order to consider if it applies. Such definition may be provided in national Laws. 

As an example, the Australian Copyright Act 1968 https://www.legislation.gov.au/Details/C2017C00180 Division 3 defines four "exemptions" to the necessity for permission from the Copyright holder:

• purpose of research or study (Section 40)
• purpose for criticism or review (Section 41)
• purpose of parody or satire (Section 41A)
• purpose of reporting news (Section 42)

I would simply say that you should not assume you "know" what any of those mean

.. but it is being used for education purposes

Now that is an interesting aspect which falls under the aspects of "fair use" or "fair dealing" mentioned above, and will have some national basis of interpretation.

Again, clearly the basic principles of Copyright ownership makes no distinction about how or why someone else may want to use the document.

The process of distributing the material is under the EXCLUSIVE control of the Copyright holder.

However in some countries, the Copyright Law may provide some ability for using Copyright material for education purposes ... but again, this has certain limits.

From what I have read, educational purposes are still only in respect of the student themselves.  In some countries, the student may be allowed to copy and use such material for their own purposes WITHOUT seeking permission from the Copyright holder. In this respect we can imagine as an example that possibly means including a diagram from the copyright material in their thesis.

However again from what I have red, use by the academics (professors, lecturers, tutors ..) to include something in their lecture notes and presentations is still subject to requesting permission from the Copyright holder.  This makes total sense as any of us could claim we have used material for the purpose of educating others and so such a "loop hole" has been closed off.

Supporting Copyright, "calling out breaches"

So there you have it.

I strongly believe in the rights Copyright provides the Copyright holder.

I strongly believe in the expectation in professional ethics, and just general morals, for others to respect Copyright restrictions and permission requirements.

Unfortunately the policies of public forum web sites (e.g. LinkedIn) often only allow them to take direct action to remove offending posts if the Copyright holder directly objects. https://www.linkedin.com/help/linkedin/answer/394

However, Copyright holders tare are always very happy to have been notified about potential breaches and state they will take appropriate action.
Of course "appropriate action" is a whole world of issues apart from having the post removed when the loss of Copyright holder income is taken into account! 

I also accept that the whole area of Copyright is easily misunderstood ... and reading the Australian Act, or your own national Laws, is not an easy task as the learning process.

Perhaps this serves to help you in some way.

If you still don't "get it", consider this scenario example:

You have toiled away for months, even years, writing a book (of any sort) and have it published for sale as something useful for the industry or community at large. 
In the process of publishing or subsequently, it is created in an electronic form by some means (intentionally or unintentionally on your part, approved or not approved by you) . 
However that electronic document is posted on LinkedIn by someone else.
Anyone can therefore open the book in full-screen mode and download it for free.
The income you (and your heirs for the next 50-100 years) had hoped to receive as the reward for writing the book is now reduced, perhaps even to zero!

But clearly this brings home the relevance of respecting Copyright as part of "professional ethics", to the extent that those breaching the Copyright are demonstrating at least some disregard for professionalism, which may in fact bring into question their wider professionalism .. I will leave you to make your own opinion and carry out your own investigation of that! 🤔

The questions are: 

1. Are you happy that everyone else "turns a blind eye" to the breach of your Copyrighted material and says nothing? 
2. Would you prefer that someone speaks up and calls for the breach to be removed?

I hope this all helps you accept, perhaps even support, my efforts to highlight Copyright Permissions .. feel free to make your own comments about potential breaches 🖊📝 and/or respond to mine where you see them.

The more is said to the of Copyright abusers, the more the abusers might "get the message" and desist from such activity without first obtaining and advising us of the required permission ... 👍👌.

Extra Notes: