Note also that if you try to join a group in progress to help a friend, find it's the wrong one, and try again, you will either be offered the same group again or else run the risk of the penalty that affects players that queue for dungeons but do not enter them when the queue pops. I think that being able to invite specific players would be good, although it would make the "get to last boss and kick someone to invite lazy girlfriend/boyfriend for an easy kill" start easier. It's worth it if it helps fill broken parties, I suppose.