Use mixing valve to vary water temperatures to different parts of home. The laundry room can receive very high temperatures for wash day, while bathrooms receive lower temperatures for kids safety. This is possible only when hot pipes are run separately to different parts of home. The mixing valve has adjustable temperature sensor, and adds cold water to the hot water line to keep water at correct temperature. So the hot line going to kids bathroom is connected to mixing valve, while laundry room receives fully heated water straight from water heater.