Peggy
I've always left my fresh water pump on from the time I come aboard till I leave the boat. In fact, even when I was away from the if the ice maker was empty when I left. As long as it's on, there's -0- wear and tear on the pump except when a faucet is opened. Otoh, every time it's turned on it has to work to repressurize the system. The more work it has to do, the shorter its lifespan.
It makes no more sense to turn off the water pump on and off every time you need water or overnight than it does to turn off your water at home at the meter when you leave for the weekend.
However, NONE of the above applies to dock water connections! Dock water should be turned off ON THE DOCK any time you leave the boat, even for an hour or when you go to bed. 'Cuz there are only two kinds of pressure reducers--those that have failed, and those that will...and you need to be aboard and awake to hear the FIRST sounds of gushing water in the bilge when it does.
I know more than a few folks including both myself and Tim R. another forum member who have lost all their on board water when a hose parted, failed or leaked.
In my situation the hot water outlet hose on my hot water tank blew off the fitting because for some reason Catalina did not use a barbed fitting.

We were anchored off an idyllic Maine Island stuck with no water. It ruined our day to motor in no wind 16 miles to fill up with water again after repairing the leak. When we were off taking some photos in the dinghy the water pump drained our entire supply into the bilge. If we had not come back when we did we would have burned out the pump or killed the batteries.
Boats are very different from homes but even I turn off my house water supply when we leave for a weekend or a vacation. In Maine we have this thing called winter so for many turning off the water supply when they leave is not uncommon. Loose power but still have city water pressure and you'll freeze and flood your house. Turn off the water supply and all you'll do is freeze the pipe..
Homes do not move or vibrate nearly as much as a boat does. Many boats use cheap PVC water hoses and have water heaters heated directly off an engine that can reach a dangerous 180 degrees, or what ever the operating temp of the engine is, causing tremendous pressures on these cheap PVC hoses.
Turning off the pump is prudent practice for more important reasons than just the lifespan of the pump. Tim R. & I are two prime examples of why and we are also both quite fastidious about maintenance of all systems. If it can happen to both of us it can happen to anyone. When we are in the cabin hanging out or making breakfast, lunch or dinner the pump stays on when we are underway it is off and when we go to bed we turn it off. We have a switch to turn the pump on right in the galley so it does not require a trip to the panel.
As for short pump life I'd worry far more about the vast majority of boat owners who don't use an expansion / accumulator tank to reduce pump cycling than I would about the ones who flip it off when not in use for safety reasons. In our current boat if we drained 85 gallons of water into the bilge we'd loose more than just water, we'd severely damage the cabin sole and other items. In an ideal world boat plumbing systems would be as reliable as home systems but the environments are totally different and unfortunately they don't seem to be..
My boat is now PEX plumbed, not cheap PVC, but I still turn it off when going to bed seeing as Tim's failure was under the cabin sole where he could not see it...