It's not just the group chat that is utilized by joining groups, in fact, most of the time I rarely use the group chat unless I have a specific need. Groups are also utilized by people for receiving notices from favorite stores and vendors announcing sales and specials and for clubs announcing events. Within clubs alone, they may utilize several groups to manage different aspects of the club and access to items or areas. Land owners may setup separate groups to manage different parcels on a sim(s). When you work at several places and/or own land in several different areas groups can add up quickly. That I believe is one of the number one reason we need to be able to join more groups... not nessesarily the group chat aspect.