Axios:

Even when you’re cautious about sharing, Facebook’s dossier on you will be hefty. Facebook tackles its mission of “bringing the world closer together” by creating a map of humanity, and each of us represents a tiny node on this “social graph”.

Facebook’s privacy policies reinforce the message that “you have control over who sees what you share on Facebook.” But if you use Facebook at all, you don’t have much control over what Facebook itself sees about you.

There’s no doubt Facebook knows more about you than you realize but it also knows a lot about you that you gave Facebook voluntarily.