Anybody here ever heard of unsprung weight in a car? It's the rims, tires, brakes, hubs, and portions of the strut. If you can shave a couple pounds of unsprung weight off a car it'll make a real difference in lap times.
I love that you used this example because I have done a lot of research on this for my car. Cost is not worth the benefit, but it is funny to see how much people will pay to reduce unsprung weight and rotational mass. It's extra funny, because the newest model is about to be released in EU (VW) and the new chassis is supposed to knock off 600 lbs from the car... People are paying 600 dollars for lightweight flywheels and 1000s of dollars for lightweight wheels that give them maybe 20 lbs weight reduction and 10 more hp at the wheels.