Tony:

Good point you raise. I had the very problem you addressed in the late sixties. Every weekend when I went out to the boat, I found an increasing amount of water and couldn't figure out what was going on.

My experience is that those leaks start small and accelerate. It is for that very reason that I don't want the pump on when I am off the boat. If there is an inordinate amount of water, I need to fix it pronto.

On the other hand, if the leak is massive and sudden, the boat will sink regardless, since the battery will be shot in not much time (the pump draws 20-35 amps).

So the answer to your question is that I turn off all electrical (the main throw switch) when I leave the boat, figuring it is more important for me to know that my battery is fully charged when I return.