None of my sons is on Facebook, as they distrust it. Well, one had to join some years ago because of a project he was working in, but AFAIK doesn't use it now.
If you read the book "The Circle" by David Eggers you would certainly think twice about it. It's an awful book (badly written, illogical plot-line) but the basic idea could easily be the truth. I think they're making a film of it.
So far I have managed to escape its claws, although I reluctantly joined Whatsup because that is how our choir, and the girls at work, are all connected.
It doesn't worry me personally if my data is out there for others to find, but Son No 1 is dead against anything like that, and he ought to know as he is a nerd who lives and works in Silicon Valley.
But so many millions of people are now on FB that it probably doesn't matter any more. Go ahead and join, it is certainly a way of keeping in touch especially with people who are housebound or not so mobile, and who are lonely because of that.