I don't leave mine on for an hour but I do leave it on to give the kidlet his snack or throw in a load of laundry and bring one up or something. I don't think I've ever left it on for an hour,though.
I think it is hard on the machines to continuously turn on and off. And if you've done a bunch of adjustments that you don't want to save then it is just easier to leave it on, I think.