As
@nickyboy says, LinkedIn is far more useless, annoying and intrusive. I got rid of my account about a year ago.
Facebook, for all its well-publicised problems, actually performs a useful service. A couple of my colleagues have made their names with research and claims that we are 'the product' of Facebook, but it's actually not anywhere near as simple as that. The thing is that you have to learn how to make FB work how you want it and that takes some time - as with any technology.
But it can get addictive. At one point I had well over 500 'friends', most of whom I actually had only a passing acquaintance with and no interest in. So a couple of months ago, I culled the list, reducing it to around 150 people: most those I had actually met and liked, some family members, and colleagues whose work and comments I find interesting. I only very occasionally will add another and refuse all unsolicited requests for 'friendship'. And I keep it quite sectioned, posting work stuff only in the closed group that I'm a member of, and only allowing friends to see most of what I post. I also have a little app which stops most FB spam. I don't list my date of birth, place of residence, relationships or anything like that.
As a result, I get very little spam, almost no stupid posts and family pictures only from those families I'm actually interested in. It works for me. If FB get some marketing capital off that, I really don't mind. But judging from the ads I get, when I occasionally bother to look at them, they don't even seem to realise that I'm married and have a son, so their surveillance algorithms can't be that impressive.