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So if a protection operation trips the CB, the only way a Master/Slave would know about it is if the Master, by chance, asks the Slave what is the CB position whilst the CB is still open.
If in the meantime there has been an autoreclose before the Master polls for the status, the next request from the Master will result in the Slave simply sending back that the CB is (apparently still) closed - the fact of the CB opening and reclosing is missed. 
The Master would have to poll other information to eventually detect that a protection trip occurred followed by the reclosure.
Client/Server does everything Master/Slave does as above PLUS the Server can automatically send information to the Clients
So the Server can be configured to send a Report to the Client(s) every time the CB position changes - noting the Report can be configured to be sent to multiple Clients.
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Client/Server Buffered Reports means the Server effectively verifies the attempted message does in fact get through to the Client. If it doesn't get verified as reaching the Client, the Server puts the message in a buffer and keeps retrying to send it until it is verified (or it is overwritten as a buffer full).
