I used to work with a microprocessor driven product. It is surprising how much mechanical switches can bounce on closing. I always wire limits, float switches, etc. to operate by opening, less bounce. A broken wire looks like the limit is hit warning you that it isn't working. Otherwise you could crash into a non-functioning switch. A broken wire indicates a tank is full, warning you that it isn't working before you over fill it. It pays to always think failsafe.