Hi CavanStudio,
I would say: public rooms are... ehmm.. well, public
I think that, generally, if there are people already playing, anybody who enters to do its own thing does act rude at least. That goes for all sides, so if you are there with the band it's rude if some guitarist and drummer join in and do something totally unrelated to what is already happening in the room. And also the same opposite, if you and your band join the room with already two users jamming (allowing 8 users for example) and you start to 'practice' your music on top of their playing. I hope you understand what I mean.
Even if technically possible (anybody can mute each other parties..., but even then vote for tempo and interval is for all in the room
) ethically unacceptable.
What you can do is to find an actual empty public server, join to fill in all available user's slots so nobody else can join later... But be aware that all activity in public servers is recorded or at least mix can be listened while not joined in room (so "listeners" can listen to jams).
So if you need privacy, private server is the only option.
BTW, I already offered my private server to try and/or use