Yes, heating water is energy intensive. This is partially true.
Heaters are energy intensive.
It is pretty easy to figure out that if it is 20 degrees outside in an elevated shallow dish, that water is going keep cooling down, keeping the heater on longer. I doubt that you would use any less electricity lighting your house for the holidays. Also, because we stay fairly mild here in the PNW, it would only run for days at a time. If you are willing to go out in the cold every night to unplug it. The electricity a pump uses is minimal.