There's probably nothing wrong with just letting the coolant circulate. The tech help lady at Atwood confirmed this for me a while ago. She said, like you said, it is designed for that kind of usage.What is the downside to just letting the tank get to max temperature? That is what it is designed for. The mixer value on the output should keep the tap water at the right temperature.
On the other hand, many times I don't want to heat water. Maybe I haven't filled the water system or maybe I'm just using the van for whatever. I found, with other motorhomes I've had, that heating water and not using it makes for stinky water. I have ball valves to turn off the flow but it would be cool to control that from inside.