What you seem to be describing is the maximum theoretical efficiency. It's a common thing in lots of fields, and it's valuable because it gives you a goal you c

What you seem to be describing is the maximum theoretical efficiency. It's a common thing in lots of fields, and it's valuable because it gives you a goal you can aim for, and know that you have reached the theoretical limit of performance. As a director of mine once put it, it's important to know when to stop [trying to improve something]. For example, the Carnot cycle gives us a theoretical maximum efficiency of a thermodynamic engine, and the Cramér–Rao bound gives us an upper bound on how much accuracy we can extract from noisy measurements. I don't know what this would be, or how we could determine this, in the graphics world, but it's still a very valuable and interesting idea.