I’m constantly running into multiple groups that address the same subject. It would be nice if I could combine those so I saw all the posts in one place. For example, all the forums that are discussing UAPs it would be cool to just look at a single thing that combined them all. 
I believe this is closely related to how we manage numerous communities that focus on the same topic. It’s likely that many of these communities have little to no activity. Eventually, I suspect Lemmy will face a real problem with this given no cross community/instance admin role.