A slider appears in the guest’s settings menu.
This feature could be useful for guests that have limited CPU or Network bandwidth to self-regulate.
Lowering this slider will reduce the video bitrate of incoming video streams.
It will not allow the guest to increase the room bitrate's limits; only lower them
I suppose while listed as a 'viewer' setting, you need to be a publisher also to access this value (as the settings button is needed).
Consider using &totalroombitrate if you wish to increase the bitrate higher than the default max of ~ 500-kbps.