If you look up the practical application of Shadow profiles they have the ability to gather information about non-users, which also includes unborn children in the case of them discovering that the mother is pregnant through whatever web searches that they may be doing even outside of Facebook. The whole science of Shadow profiles used to strengthen the algorithm is incredibly frightening and part of the reason why I left Facebook.

It was that combined with the fact that they create shadow profiles for your unborn child when your wife is pregnant. (Found out through FB being allowed to track your browsing history even off the app). That was the final straw right after the Cambridge Analytica issue.