This info can be found here - https://support.f5.com/csp/article/K13310
Pertinent points being...
When set to Disabled, a node or pool member continues to process persistent and active connections. It can accept new connections only if the connections belong to an existing persistence session.
When set to Forced Offline, a node or pool member allows existing connections to time out, but no new connections are allowed.
What is the case when one of the member is not taken down by big-ip administrator, but one of the the actual member server is either shut down or is restarting? How will existing traffic to that member behave?
If by default it rebalance connections to other available member, will the users connection to previous member (which now has gone down) disrupt momentarily before moving to another available member. how will the user experience be in this case?