I find it useful to see what's going on with friends and family. When I get friend requests from people I don't know, I just ignore it. I don't have my FB posts as public, friends only. Lately I've spent less time in it as it can be a real time waster. I get the impression that for some, all they do is spend time in FB through their cell phone computers.
There is some good in it if one limits their involvement to a smaller circle of friends and family, at least that is my perception.