Perhaps I am generalizing too much - what I truly meant was this feature enables Facebook to have even more fine-grained criteria on which to sell ads.

Which criteria?

Criteria like age, location, education, interests etc. You can see the entire list when creating a Facebook ad: http://www.facebook.com/ads/create/. But the advertisers don't get to see what belongs to who, unless someone clicks on an ad, buys something and they backtrace all of that. They only target it.