This is a quite from a Facebook employee:
We’re blind. It doesn’t matter what any individual person thinks about something new. Everything must be tested. It’s feature echolocation: we throw out an idea, and when the data comes back we look at the numbers. Whatever goes up, that’s what we do. We are slaves to the numbers. We don’t operate around innovation. We only optimize. We do what goes up.
There is a flip side to this too, right? Facebook HAS that kind of data. What I wouldn't DO for that kind of data. Do we have our own custom tracking (Google Analytics) on our magneto sites at work? Of course. Does it get us the data we need? Yes and know. We can track conversions, user flows, A/B test what we need. But, the pixel level knowledge of HOW a user is using the site that Facebook seems to have seems pretty slick.