Why it matters to you
On the rare Greater Houston nights that drop well below freezing, aux heat can run for long stretches, and resistance heat turns each unit of electricity into one unit of heat while a heat pump moves more heat than it consumes. Seeing "AUX" on the thermostat on a frigid morning is normal; seeing it on mild days is worth a look.
Practical guidance
Avoid deep thermostat setbacks in heating season, since recovering several degrees at once is a common trigger for aux heat. If AUX stays on in mild weather or the house cannot warm without it, have a licensed technician check the heat pump; heat strip and wiring work is not a homeowner task.