From a user point of view there's definitely that initial rush of 'wow, this group looks great!' to scanning across to see 0 posts, 0 comments, 0 users access feeling sad...
That's not too say that these should necessarily be removed but it's a lot harder to get people in to niche communities. Unless you outright went into the Reddit equivalent and said politely you were trying to start one here. But they'd probably be happy in Reddit by this stage so...