Facebook saves our keystrokes. A record exists even if the user decides not to post those keystrokes. Essentially, Facebook tracks self-censorship and wants to minimize it. Jennifer Golbeck doesn’t like this very much (I added the emphasis):
Facebook studies this because the more its engineers understand about self-censorship, the more precisely they can fine-tune their system to minimize self-censorship’s prevalence. This goal—designing Facebook to decrease self-censorship—is explicit in the paper.
So Facebook considers your thoughtful discretion about what to post as bad, because it withholds value from Facebook and from other users. Facebook monitors those unposted thoughts to better understand them, in order to build a system that minimizes this deliberate behavior.
Let’s clear something up. Users are not Facebook’s customers- we are the product. Facebook maximizes its own value by minimizing behavior that decreases our value. The more we share, the more valuable we are.