https://www.vox.com/policy-and-politics/2018/4/11/17225518/mark-zuckerberg-testimony-facebook-privacy-settings-sharing

People can use the “share button” for some data control. But what are they giving up when they just log into Facebook?

Mark Zuckerberg really wants you to know there’s a button there for you to decide who among your friends and acquaintances sees the pictures, messages, and news articles you share on Facebook. He’s less willing to talk about how or if you can decide what advertisers and marketers see when you log into Facebook in the first place.