There's different rooms such as certain state rooms, media rooms, etc. Some I have been removing due to either just one user, just generally dead, the owner of the room has never logged in since 100 days ago, etc.
People can make their own rooms and they can encrypt it and also hide it from the channel list. Such as making it invite only.
For vetting, it's why I have the thread about requesting to sign up and I check their activity here. Now I'm noticing I still have waiting tokens from the ones I sent to and they've been online here from the past few days. I get people are busy, but they only stay active for so long till the tokens expire.
I've actually pushed some to expire within 2 weeks instead of one.