I've been admining and moderating boards since 1993. Many boards, especially active ones, have separate threads where people can 'try' to be funny, rant, rave, hook-up (read: 3>). In a theoretical sense foo fulfills that purpose here. The pragmatics of it though is that BF is so large, with so many active communities foo is a separate universe. People want to keep it in here because these are the people they know. That kind of pressure release valve is a good place to move off topic stuff, racier humor, and eventually people will likely just gravitate there.