I have a fish in my apartment. I do not want him to die so I leave the heater on in my apartment and have it set to 65 degrees.
Leaving the heat set at that temperature suits me just fine. The fish stays warm and my apartment stays warm enough so that the plants don’t die and the pipes don’t burst.
Of course I could just have the heat turned off but that would mean that my apartment is freezing and I would be very uncomfortable. With the current settings my apartment feels just warm enough to be above freezing and if I wear socks in the house in addition to my fuzzy clothing I do not feel cold.
If my fish is still fine then I am able to keep the heat on the current settings and thereby save a little bit on my electric bill later on.