There are two reasons why I still visit Facebook from time to time: birthday reminders and making myself feeling worse after seeing what my contemporaries achieved.
I know the latter is unhealthy, but I just can't stop it. It's my damned curiosity, I need to know who graduated, or got engaged, or moved somewhere nicer, or bought a car... even if it'd make me feel worse after finding that out.
Oh, and there's surely some other uses for Facebook that make me still keep it, like the Marketplace (which I never bought anything off), but I can't think of them all right now.
Also, I set up my social media so my Instagram account is for cars, friends and people I recently met, Facebook for older acquaintances and friends, Twitter for tech, Reddit for when I need help (when it comes to stuff like tech, buying online, personal grooming and style, etc.) and YouTube... well, for music (old habits die hard) and tech stuff, again. Although I use YouTube privately 99% of the time, so I don't even use my two YouTube accounts, private and 'public' one.