Negative. Think of all the flips that you have seen. Elliot Sadler, Ryan Newman, Rusty Wallace, Davey Allison, Bill Elliott Darrell Waltrip. They all flipped becuase there cars dug into the grass. You can not dig into concrete and in most cases your accident would look like Dale Earnhardts when he flipped at Daytona once over and that is it. Did Davey Allison not flip at Charlotte on the concrete just once? When you flip on concrete your initial flip would have to be from another car hitting you. It most cases there is not enough momentum for that to be much but the wind underneath the car would do the rest to turn you over. After that you would have slowed down enough for the car to not flip over again but on grass the car would continue to dig which would cause the car to flip over and over again. The benefits outway the negatives. How many times have you heard drivers say that the car actually picks up speed on grass. IMO the tracks do not want to do it because it will not look pretty. Cost is another but then you would not have to maintain the grass.