It would be nice to be able to duplicate a group with the existing users, or at least a way to pre-poulate a new group using a set of users from an existing group.
I ran into a situation where I created a Segment that I wanted to share to users who have access to the suites affected, I also wanted to give the segment to the "All Report Access" group, however, due to the nature of being a pre-defined group this was impossible. I had to create a new group with the same set of users to ensure that everyone received the segments. This meant I had to compare the "All Report Access" group to my new group and add 74 users one by one from list of about 200 users.
Since I didn't set up most of these groups, while many of them may have been in other groups, I didn't have time to go and review all of the users. Having this ability to duplicate a group and make manual modifications would be a very handy and time saving feature.