Sets a room ID for the session to join
Rooms broadcast to all participants who have joined.
Rooms limit the viewing bitrate that guests of a room can request. OBS does not have these viewing limits though.
Rooms have no forced limit on the number of guests allowed, but practically 10 is about the limit I'd recommend.
There's also a video below looking at what sort of performance and system load there is when using an unoptimized group room.