What is the rationale for calculating relative impacts per acre instead of per unit output? This appears like a hustle to make organic agriculture look better t

What is the rationale for calculating relative impacts per acre instead of per unit output? This appears like a hustle to make organic agriculture look better than it is. I am prepared to be wrong about that, of course. It isn't completely beyond the realm of possibility that there are legitimate "dilution is the solution to pollution" effects at play. I just... have doubts.