"Max number of recently active clients" - details

I’ve got a question about this option “Max number of recently active clients”. In the manual it’s stated that this option limits the number of active clients that can be accepted by the server, whereas active client is the one that has been seen in the last two months.

If someone could explain in details how this option affects the performance and the inner working of the UrBackup, I’d greatly appreciate it. Thanks in advance.