I'm confused as to when to use thermocubes. If you use an aquarium heater, do you need a thermocube? What about a bird bath heater? What about a stock tank heater or pond de-icer? I'm not sure I understand. Like I guess some things has a built-in thermostat & will kick on & off on it's own without a thermocube & some things need a thermocube or else it would stay on constantly?