I have a heat pump system with electric auxiliary heat (heat strips). My thermostat is a Robertshaw 300-208. This thermostat can be set to lock out the heat pump whenever the aux. heat is on, or to let both run at the same time. I've set it to lock out the heat pump. My reasoning is that if it's too cold outside for the heat pump to maintain the set temperature without aux. heat, then the heat pump isn't contributing much (if anything) anyway, and it should therefore be switched off while the aux. heat is on to increase the longevity of the compressor.
What do you guys think? Is this a good approach?