NM 2.2 on Windows server

Ok, I'll rephrase the question...

The DefaultPolicy has an option to "Archive message sessions". In our case it is enabled and locked.

When creating a new Chat Room there is an option on the General tab to "Always archive". By default this option is not enabled. The documentation states that the setting is optional and gives no clue as to its relationship to the DefaultPolicy setting mentioned above.

So, what's the difference between the policy-level setting for archiving messages and the chat-room-level setting for archiving chat room messages?