Suburban Water Heater AC switch at the water heater

I've always wondered why the switch is mounted on the water heater. I also have a switch in the kitchen that kills the power to the hot water heater. I usually just leave the one on thats mounted in the hot water heater. From what I read it sounds that some the 5ths only have switch on the heater. I've always wondered why two switches on the system. Guess I now know.