It does two things for you: a) you get to visualize and explore the image layer by layer, and b) it will analyze and score the image with a % efficiency, listing all of the potential "inefficient" files.

In this way it's not just showing you a score... the score doesn't help you make the image any better. This is why letting the user explore the layers is good, to help discover and explain why there is an inefficiency (not just that there is one).