I unplug mine during late spring, the summer months, and early fall. It's warm enough here in SoCal to let the temperature maintain itself during those times.
Phoenix here, I keep my temps in the high 70's during the winter. The heaters might click on two months out of the year. The rest of the time I keep them unpluged.
My mini-reef has one, set to 70 should the ambient temp in the apartment drop as I like things cool. By the way, for all of you ladies out there, my winter coat is coming in thick this year. Just in case anyone needs to stay "warm".
My planted and axolotl tank run without heaters, but the lights keep the temp up. Good cycle of cool/warm.