Could be upsides to that, but cranking up the global food requirements (remember, a muscular body requires a lot more energy to maintain) would be a negative.

Also, what's optimal? Your body adapts to what you are doing, something we take for granted today. E.g. If you like bicycling, a permanent linebacker build may be undesirable.

It would probably be more ideal to set some kind of fitness "floor", rather than remove the mechanism completely.

Most people already eat much more than they need, might as well make use of those calories.

Of course there should be a "floor", we don't want to grow into blobs of slithering muscles and veins, just well-built.