It also depends on how you use Facebook.
I've noticed that people who use it to share political posts, rants, etc. tend to be some of the most emotionally negative people I've met. (reposting stuff entails low thinking effort)
Whereas people who write little David-Sedaris-like stories about their lives, sometimes with pictures, tend to receive positive emotional benefits. It's like the practice of writing Christmas letters but instead of doing it once a year, you get to do continuously. Sure there is the occasional flexing and humblebragging, but even the most humble among us can't help but share our little life victories on occasion (e.g. Ph.D. graduation, vacations taken, etc.). In my circles, people tend to share stories about their foibles and flaws too, often in a funny way, so it kind of balances things out.
Facebook is an especially great place for introverts to be vulnerable through the medium of the written word. In real life social settings, introverts tend to be crowded out by others and can sometimes struggle to tell their story. When we're in a face-to-face situation, there isn't always the occasion to truly share in detail because the politer ones among us want to avoid hogging all the attention. And even when the spotlight is on us, we don't always remember all the interesting stories to tell.
That's why the written form is so powerful as a tool for self-revelation and vulnerability. It helps deepens relationships. I've had friends who've read my posts come up to me in person to tell me, "I never knew that about you", which actually made it possible to have deeper in-person connection.
I do have a few rules about posting: if I didn't write/create it, I won't post it; and before I post, I ask: "is it kind? is it true?" These rules seem to keep me out of trouble.