FB is important in letting me keep a full but just-in-time social calendar. I don't want to plan going out a weeknight far in advance, or even necessarily a big night on a weekend. But often I do want to go out. Facebook makes it easier to organise these things at a moment's notice. This is much better than planning ahead, because if you plan ahead you have to keep appointments even if you don't feel like it on the day. So socialising a lot that way gets to be a bit tiring. Doing things on the spur of the moment is better.

For example, the other night a friend hosted a vegan potluck for about 10 people with about four hours notice. That would've been hard to do without Facebook.