[primigenus]

My interpretation is that Facebook is more valuable if the content you see when you interact with it is more useful to you. Facebook is about connecting you with family and friends, and that's easier to do if you see valuable content more frequently than low-value content (which might pop up in a simple chronological stream).

I think this way they're trying to improve the "keep-alive" of relationships between you and people on your friend lists by showing you more valuable content, which in turn will lead to higher engagement (eg. likes/comments/etc), which in turns keeps relationships going through interactions, which in turn keeps you coming back to Facebook. And that obviously is a good thing for Facebook.