With very active factions, private forums can be a good thing. Players can delve deeper into the environment, discussing politics, the economies of Sirius, and who the latest troublemakers are.
Granted, this can also be done here, but... if 2 or so factions are posting in their message dump 5 to 9 times a day, it starts stealing the thunder away from other, not -as- active groups. That and, said groups don't have to deal with repeated accusations of metagaming when they theorize and form potential game plans in public view.