For starters, you are giving them your picture (so that Clearview can grab it and use it for facial recognition, to recognize you as you go to places) and your name, as well as some of your social graph.

Above all, you are giving them your attention and your time.

I deleted my FB account 3 years ago, and so far nothing bad has happened to me.

It's funny that I was among the first people to create an FB account when they opened it to the general public, and some people would judge that I would use it. And now people are going to judge that I don't use it? Whatever. If anything, that makes us pioneers and trend-setters, not "suspicious".