After the last clustering post, Stop users accidentally connecting to passive Domino cluster servers I've had several people ask when I would use SERVER_RESTRICTED as I'd indicated I would not use that to keep users off my clusters.

Well, let's look at this scenario where you are running an active-passive cluster (that is one server handles all user requests-the active; the other handles fail over when the active is down-the passive):
1.        Your active server goes boom for whatever reason, hardware, crash, virus, asteroid hit..... Users fail over to passive.
2.        You replace, repair or otherwise get active back online and the server is up and accepting user requests.
3.        To get users off the passive and back to the active I would add SERVER_RESTRICTED=1 (or 2, 3 or 4 see below) to the passive server notes.ini. This will redirect all new open database requests to the rejected and forced back to the active. Users with active requests continue as usual on passive.
4.        I would let the happen for a few hours or days then drop all users off passive after hours.
5.        I would then remove SERVER_RESTRICTED from the passive notes.ini and let SERVER_AVAILABILITY_THRESHOLD on the passive protect is from users drifting back to it. All users should now be back on active.

You can also use this technique to force users off an active and onto a passive for maintenance reasons by applying basically the same theory.

This is not to say this is the only use for SERVER_RESTRICTED, but it is what I use it for. Note that there are multiple options for SERVER_RESTRICTED (1-4) and these are documented in IBM Technote 1089278 and what you choose will depend upon your outage reason.