Hitting the grass kills your momentum, a lot, but equally so does sliding round corners. While it looks cool, it isnt going to help you win your races one bit. If you go in a bit hot and youre not going to make your turn in for the apex of the corner, let it run wide and use all the track. It may cost you some lap time, but its going to cost you a lot less than if you overcook it and get the tail out. If youre too late on the brakes, keep your turn in as smooth as you can, and youll come out better in the long run.