Risk assessment isn't just about a single event or a single night of running a pump. It is about the probability of the event occurring vs the recurring cost of risk mitigation. So if you turn on your pump every time it gets below 32F even though there is zero probability of a freeze event occurring, that is simply a waste of money without any benefit. As temperatures drop and/or duration of time below 32F lengthen, the probability of freezing increases so the benefit of running the pump might increase. However, not every freeze event results in a damage event either.
For example, if the probability of freezing when temperatures drop below 32F is 10% and the probability of damage is 10% of that, the probability of damage is only 1% of the below 32F events. So 1 out of 100 days there is damage. If it costs $1 per night of running the pump, the actual cost of the insurance is $100, not $1. But in many cases, the probability is far less than that even when temperature get down to the low teens which means the cost of the insurance is much higher.
In 2012 we got down to 13F and there was no damage to my equipment even without running the pump. But I knew ahead of time there wouldn't be any freezing of my equipment. Time to freeze was 14 hours under those conditions, and we never have freezing temps longer than about 6 hours.
All I am suggesting is that it can be an waste of money to blindly run the pump the moment temperatures drop below freezing. With little effort, you can reserve running the pump for those conditions where there is actually a probability of freezing. At that point, it might make sense although the probability of damage is still fairly low.
