Not rotating the tires will not affect your warranty. It won't affect anything else but the wear on your tires. Because our cars are front wheel drive, the front tires will wear sooner than the rear tires if the tires are left in their respective positions. And if you tend to corner aggressively, the front tires will definitely wear sooner; especially on the outside shoulders of the tires.
Rotating the tires helps to even out the wear across all 4 tires so you can replace them all at once and have some predictability on the performance of your tires.
I rotate my own tires when the car needs it. So I don't pay others to do something I can do easily. But on my BMW, I cannot rotate the tires front to back as this car is not a square setup. The front tires are narrower than the rears. I'm running 225 width up front and 245 width on the rears. I think the Michelin Pilot Sport 4S tires I run for summers allows swapping Left/Right as the tires only have a provision to have one side of the tire to face outwards. The winter tires I have for the car which are Bridgestone Blizzak WS80s are directional. So I cannot even swap them Left/Right.
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