Its complicated, as at first you ran as how as you could to maximize the amount of hot water you had, then there was a period where it was seen as more energy e

Its complicated, as at first you ran as how as you could to maximize the amount of hot water you had, then there was a period where it was seen as more energy efficient and prevented burns running at lower temperatures. "Modern" practice in this case started somewhere around 1970 where you have a termostatic valve (also called a Tempered Water System) to regulate the temperature of the resulting hot water to non-scalding levels.