Preseason football, by and large, is unwatchable. No real schemes, mostly second- and third-stringers, and half-full stadiums. On the other hand, preseason is the first chance we get to see NFL rookies on the big stage. So in fantasy land, preseason games can provide invaluable insight to the unproven players that we may just be (over)drafting in a few short weeks.
There are two glaring examples of preseason breakouts that translated to fantasy breakouts as well, and one of them bleeds blue. I will never forget these performances, and they info gleened from actually watching the games lead me to own Arian Foster and Victor Cruz in most of my fantasy leagues in their breakout year.