As said, depends on the game and personal preference.
For most, balance will be less critical for games shot with a premounted gun. Relative to all my other shotguns, my trap guns are quite butt-heavy. The butt is a convenient place to add weight and it's firmly anchored in my shoulder so I don't have to move it around. It takes only 2-3 ounces strategically placed ahead of my lead hand to alter the swing and achieve the gun movement I want. OTOH, since I start the mount from a low gun hold on sporting clays/FITASC as well as hunting flushing birds, balance becomes much more important. I have to lift the entire gun to my cheek and shoulder with as little waste of time and effort time as possible.
As I lift the gun to track the target and mount the gun, a more evenly balanced gun allows my hands to move in synch and keep the muzzle on the target line. Too much weight at either end contributes to a see-sawing movement which robs me of time and precision.
Again, like dozens of other variables in shotgunning, it's a matter of what leads to individual success. And there is no shortcut to trial and error.