I see both sides... When running a RBBC, and RB's are getting split workloads, YPC is a good start... But to mrags point- it's hard to rely on a RB that averages less than 2 yards a carry for 3-4 series (or more- sometimes less) and then busts off a run for 40+...
I would rather hitch my wagon to someone like Fred who consistently churns out 3-4 yards every time he touches the ball, instead of the guy that it's reasonable I assume anywhere from -3 to +2... With the upside of 50+