If you invest time, it is rewarding. It's like live Market Research (a subject I like, and teach). On any given day, you get to know what a range of opinions on any topic are- extremes are there in good number, but moderates too express themselves- if you look closely.
It's a great pictorial ride-through the lives of people you like (mostly).
It gives you instant feedback on many things- silences, likes, comments, all have a story to tell.
It gets you back in touch. Random conversations on Messenger included, but meetings have also happened many a time solely due to FB- which otherwise may not have. Ex-students, ex-colleagues, and sometimes, forgotten classmates. Or new-found friends-of which there are lots.
You can innovate- I have tried, sometimes with success.
It is flexible, in the sense you can stay on it or away from it depending on your other priorities. At least, I think I can (!), though it may not seem so obvious.
All in all, it has a thumbs-up from me.