The ability to, in the list of groups in the Auto Group Join Administration, define the source WordPress role of users to add (or all) and the destination buddypress group role of users when added (admin, mod, member). This way you can define some simple mappings. For example, anyone who is a WordPress Contributor gets added to the selected group as a Buddypress Group Mod. Then you could regulate users of your network to be added to groups as mods, members, etc. VERY USEFUL!