Concerning " Why are we wasting so much potential control area on water temperatures that no one wants? ", I am a professional plumber, have been for decades an

Concerning " Why are we wasting so much potential control area on water temperatures that no one wants? ", I am a professional plumber, have been for decades and... on one occasion I was told by an aging resident of a new-build home that there " wasn't ENOUGH control area" on her brand new Moen tub/shower faucet! WOW.