Communities bring people together. In the offline sense, people gravitate toward communities because they are able to share with others and benefit from team-dynamics. This means resources can be pooled to achieve common goals. In this sense, everyone wins when they join a community that they really care about.
Companies have been in the community-management business for a long time. Athletic shoe stores organize runner clubs and bookstores organize book clubs, but the really successful communities focus on the mutual benefits to members and organizers. These benefits have to be things that the individuals cannot gain or achieve on their own, or would at least find challenging on their own.
