Without it, I have no connection at all to some of my old friends. While I don't necessarily need to be connected to them, it's nice to see how people are doing every once in a while.
LinkedIn fulfills this desire in some ways, but I don't typically connect with my "outside-of-work" friends on LinkedIn. Plus, LinkedIn has its own host of privacy issues, so it's not really a great replacement in the sense of improving privacy.
There are also the useful community aspects. I often find out about local events through Facebook. I suppose Meetup or similar sites could replace that function. But my friends also use Facebook's events to organize parties and stuff - I don't know any good alternative that's nearly as convenient.
I'm not convinced that deleting your account helps all that much anyways. You do make it harder for Facebook to listen in from your phone and things like that, but I'm sure they still keep a detailed profile on you. And you can get those benefits just by deleting the mobile app, without deleting your account.
I think the better reason to delete Facebook is the mental health issues with the whole spotlight effect or whatever that's called (where you only see the highlights of other people's lives which makes you feel like your life is boring). As long as you regulate your usage in a healthy way, I think whether you delete your account or not doesn't make much of a difference.
For now I just throw on a handful of privacy extensions (uBlock Origin, PrivacyBadger, Decentraleyes, Facebook Container, etc.) and accept that Facebook is going to know many things about me.
As a point of reference - my age group started using Facebook around middle school. So I have a lot of "friends" that I would have no way of keeping up with otherwise, and I'm not used to not having that ability. I suspect the sentiment is different for older generations who are used to losing touch with people. My parents, for example, have a couple old friends from whom they haven't heard anything in many many years. That concept doesn't mesh with the lifestyle I grew up with. It's not that there are many specific people I want to keep up with all the time - it's just nice to get random updates on random people you used to know well.