I'll provide a somewhat dissenting take here. I own accounts on all of the major platforms, and while I very rarely post on them, I have a couple of uses for them that I appreciate. My biggest use is employment. As a software engineer, I've gotten, literally, all of my jobs through LinkedIn (a professional-oriented social network.) I find that in my industry, it is almost the de-facto way of finding potential employees. I get contacts from interested corporate recruiters at least every week or two. I've also utilized its ability to show me contacts at companies that people I know can introduce me to. That has also been helpful in my career.
As far as more traditional social networks (like Facebook), I have family members and some friends, who no longer live in the area, who share pictures there, and it is nice to be able to see what they are up to without seeing them in person. About once a week, I'll log in and check on a few distant relatives/friends.
Also, while this isn't really the same thing as browsing and posting content, I do find the calling feature of Facebook messenger to provide a good alternative to ordinary phone calls, even amongst people whose phone numbers I possess! The voice quality is just far, far superior to that achievable over ordinary phone networks. (It also makes it possible to contact people when their phone numbers have changed.)
While I cannot imagine posting every single event of my day for other people's affirmation, and am not a very regular user, I must admit that they do have their place, at least in my industry and amongst my circle of acquaintances.