I never really thought about it. I suppose if you measure the life of a SM motor in actual stitches, especially if you use it for machine quilting as well as for piecing, you're going to reach the end of its useful life sooner than if you only used it for making garments, curtains, etc. It would be the same difference between the car that "the little old lady drove to church every Sunday" as opposed to the 4WD pickup the guy puts thousands and thousands of miles on every year. The car might last 50 years, the pickup only ten, but they would likely get to the end of the line with about the same amount of miles. Nothing in this world lasts forever, but most of us know that a car's engine will last longer if it's well maintained and actually driven, not just sitting in a garage. I think it's the same with a SM, take good care of it and use it well to keep it running as long as possible.