With feature branches, what is ever committed directly to master

I realize there are a lot of different Git workflows but I'm wondering
how others in this community do it.

We're using our "master" branch from our central repo (Beanstalk) as a
dev branch and we have stable branches for various release versions of
our software.

We've not made as heavy use of feature branches yet as we should have.
Once we do start using them more regularly, what kind of stuff is ever
committed directly to "master" or is master typically the place where
things are merged into from other stable/features branches?

Is "master" really even unstable at that point?

Thanks in advance! I realize this question is pretty open-ended.