Under-inflated balls are easier for QBs, WRs and RBs to handle than firmer balls in inclement weather. If NE is using a football with a lower psi than their opponent you don't think the Pats would have an advantage? Even if the misdeed seems insignificant to us it was worth it to NE to break the rules. They must've felt it was worth getting caught to get a competitive advantage or else why bother?