i never broke mine in and never had a problem, kind of depends on the clutch material, but its common sense, its kind of like a alternator belt seating... u need the clutch to surface the flywheel for a while so it runs over it smooth and grabs, if it is eaten up and not surfaced evenly and the clutch disk didnt make nice grooves in the flywheel, its probably gonna slip, but ------- breaking clutches in, open up that throttle baby and boil them bolognes