I believe the goal is to have a ferment that is in the comfortable range of the yeast.
As far as i know from reading for a few years (i'm no scientist) a yeast, when stressed and at the limits of it's tolerance for either sugar or alcohol will start producing esters and other byproducts that can taint the brew quite badly.
So maximum alcohol per brew is not the goal with most ferments, but a comfortable peak for the yeast.