We have a very large user base (thousands of users).
It would be good if a group could contain a reference to other groups since this makes maintaining groups much less tedious.
Group A: User1, User2
Group B: User65, User 98
Group C: Group A, Group B, User 142
Group C is in a sense "dyanmic" so that if another user is added to Group A then Group C is effectively updated too (i.e. I'm not request the ability to have a "one time copy" of users into a new group).