The only point at which lighter is not better is when it results in component failure. Less weight improves every performance aspect of the race car - accelleration, braking, direction change, fuel consumption, tire wear. I run a lot of ballast in my car, one of these days I will head out to a track day with all of it out and see what it does, but my experience in street cars is that 40# makes an instantly noticeable difference (on a car that weighs in at 2400, so maybe less so on newer heavier stuff).