Ground water can leak into the system. Pumps can fail. Power outages can occur. Float switches can stick open or closed. The overflow tank can fill.
Pipes can clog.
Any of the five controller relays can fail. In the winter there is nobody around. There is no water service, and the water pipes are drained to prevent freezing damage. However, the septic system must remain energized, in case ground water gets into the system. If the system fails during the winter, with nobody in residence, we want to know about it right away.