It's easier for me to check up on stuff via my smartphone's Facebook app than it is to load up the web browser, type in their address, wait for it to load over 3G because they don't have a mobile geared version of the site, browse to their updates pages or whatever, wait for it to load again, pinch to zoom in.....ETC.
Facebook = Convenience in the most inconvenient of situations.
Edit*
Applies to Twitter and Google+ as well.
Facebook = Convenience in the most inconvenient of situations.
Edit*
Applies to Twitter and Google+ as well.