YPC is only a meaningful metric when it is put in some kind of context. But the same goes for other metrics including rushing attempts. Perfect example is Chris Johnson, who gets a ton of carries regardless of how he's doing simply because his team's offense has no other real threats.

Explosive runs might be a good metric with some teams, but for other offenses the more important variable might ability to pick up consistent positive yardage on 1st and 2nd downs. Even when he was good Chris Johnson would lose yardage on a high percentage of his runs. For an offense like Green Bay's that depends on maintaining manageable down-and-distance, Johnson would not be nearly as valuable as a guy like Lacy who consistently moves forward.