Yes, running in 4wd when not needed will add extra wear on the system, but I don't think you'll notice it for the first 30 years or so. What you will notice is that you will wear out your front tires and have to replace those more often. I specifically don't use 4wd when doing most loader work because the high weight load directly on the front axle will cause a lot of tire wear and drive train binding. A lot of my loader work involves tight radius turning on relatively flat ground. Your case may vary. In short, anticipate the need, use it as needed.