Looking for activity stream set up advice

We are on 10.1 and the activity stream for the members page has some challenges.We have one group that spits out A LOT of forum posts. Very annoying to some people, despite being members of the group. If I were to change that group from one that has members to a joinless group, would that cut the flow or will it have no effect? The activity stream mode that makes the most sense to me is the Site (contextual user's joined and joinless groups only).

That bit about joinless groups is confusing. Does that mean joinless groups that the user owns?  That's the only way it makes sense to me, since how can someone have a joinless group unless they own it. But maybe i'm missing something.