For example in Mac client's sharing window here: http://prntscr.com/dar3c6
make change 'admin (group)' to 'admin (group, containing 3 users)'.
This would be more intuitive and help people to know how much other people would be affected by their decision to share with a certain group. Because groups can grow or shrink due to admin activity and the user might not be aware that his select will fire up an event for eg. 30+ people.