I deactivated my Facebook account several months ago, and it's been about 90% great, 10% frustrating. It's great for all the obvious reasons (less timesuck, less compulsion to endlessly scroll your life away, no notification interruptions). The frustrations are real, though. Primarily it's around events and photos. There are some communities I participate in that regularly organize events through Facebook, and now I…
I was almost done with college when FB suddenly became a cross-generational phenomenon and started being about more than photo sharing and event planning; I still fondly remember those days.
The one advantage I would add is the rare occasion when someone needs to get in touch with me easily: I've had extended family who lives on the other side of the world get in touch with me through FB on short notice when they were visiting my city. I could definitely imagine that some of these cases wouldn't have happened without Facebook, since they would be required to 1) know that I happened to live in this city and 2) go through probably three separate people across different continents to get my phone number. This is infinitely harder than searching their FB friends for my city and going "oh dang! wutbrodo lives there now? I haven't seen him since we were kids, I should reach out!".
That being said, all of the 90% downsides of keeping Facebook are, to some extent, within your control. I won't pretend that I'm congenitally immune to them, but all it took was a little discipline and a little time and it really wasn't that difficult to avoid the timesuck/endless scrolling/notification issues.
I've never really been able to relate to the idea of completely deactivating Facebook and losing the 10% benefits, with the possible exception of the few people who have a completely insurmountable psychological compulsion to use Facebook. This is especially true because of all of the levels of FB exposure you can have without going all-or-nothing: Chrome extensions to remove the newsfeed, disabling notifications on your phone, only visiting FB on the web and not the app, etc.