For me, it's timely knowledge of friends doing things I might want to join in on, keeping up with a few groups and organizations that post things there, and che

For me, it's timely knowledge of friends doing things I might want to join in on, keeping up with a few groups and organizations that post things there, and cheaply signalling my affiliation with just about anything by joining a group named after it. I also found a great band called "The 21st Century Monads" because I was looking through famous people's profiles, and it's the only music group on David Chalmers' page.