I am quite surprised by the number of people who leave Facebook and delete their profile. Often the so-called Cambridge Analytica scandal is brought up as a reason.
But ... everything which happened there was totally clear before that. There are many apps coming from shady sources which ask permission to access the user data and also the data of the users friends. Even users who avoid these apps themselves can be very sure that one of their friends uses such apps, thus exposing their data to third parties.
This is all known since Facebook introduced apps, it works as designed. As a consequence, a user should never create, share or like anything on Facebook which is not intendet for the public. Just use Facebook as you use Twitter ... everything you do is visible to everybody.
So where is the scandal? Cambridge Analytica used the data to allow more efficiently targeted ads. This is exactly the business model of other companies such as Google. This is also well known and no surprise and hardly a scandal.
So everybody who deletes Facebook accounts now seems to have ignored these facts until now.
Update: Wired has a good writeup how to restrict what FB and others collect about you.