Re: Break In
If you have a chainsaw or lawnmower, yes the engine goes through a break-in period. New cylinders are honed, and the rings seat.
But you don't notice any dramatic change, because you're not taking your riding lawnmower to redline, and both it and your push mower have the throttle configured so that it won't redline - if the throttle isn't just completely fixed in one position entirely.
I don't ave any experience with chainsaws, but I have to think they probably have limited throttles, too.