When I leave a room, I turn the light off. When I enter it, I turn it on.
When I leave the house, I turn the heat off. When I enter it, I turn it on. If I had pets, I'd just dial it down to "pet comfort" level while away.
Am I missing something?
EDIT: I do have a Roomba and think it's great. I hit the button when I'm about to go out for an hour, and there's a clean floor when I get back. I appreciate that. No internet required as well.