If you're not running a filter for fish, I see no reason why you can't turn it on or off whenever you want. I don't know about wear and tear on the pump by doing this, though. Hopefully someone with more knowledge about pumps will step in and offer their opinions. Some pumps, like Pondmaster, are very energy efficient, so if and when your pump "bites the dust", look for pumps that use low wattage. Some pumps gobble electricity like candy and can indeed run up your electric bill, so I can see why you would want to use it sparingly. Turning off the waterfall will not affect your plants. I have some plants in my stream which is constantly running, and other plants in tubs of water that are perfectly still. All of them do just fine.

When I went to the cellar, I found quite a bit of water around the tank. To start with you need to find where that water is leaking from and fix it - otherwise every so often the pressure drops to the pump cut-in setting & then the pump cycles on and runs until the pressure switch reaches its cut off setting - and then that leak (or the check valve) lets it slowly loose pressure and the pump runs again, and stops,,, again, again, etc. After you fix that leak if it still runs the check valve probably needs replacing but if its an air bladder tank bleed it and check the air pressure which should be about two pounds less than the cut-in pressure. Around here it seems like those check valves don't last forever but do last a good long time.

Update: I installed a Zoeller M98 and replaced pipe on inside of house and check valve two days ago. Then ran it to 25' of 2" pipe on the outside to 25' of 1 1/2" pipe and then ran a hose from that about another 30' away from the house. The time between cycles is starting to increase. When I first installed it, sump pump ran ever 10 minutes. Now it's running about ever 40 - 45 minutes.

Landed here from a Google search where I had the same problem. What I discovered is that after heavy rain/snow melt, the water table around our house rises to the level of the underground french drain, into which the house gutter downspouts empty. And then, one of our sump pump outlets is routed into the downspout near the foundation. So when the water table is high, the french drain is saturated, and cannot take on any additional water, especially the water volume from the sump pump. My decision was to install a ball valve and a cleanout T connection in the sump pump outlet, so when the water table is high, I close off the route into the downspout, and connect a 20ft long pipe to the cleanout T (it's threaded, so I use a trap adapter to screw in to the T connection) that runs out to the driveway. It's not ideal, but it works. When it rains hard or we get a flood watch, I turn the valve and run the pump water out to the driveway instead of overflowing my french drains.