A lighter flywheel allows your engine to rev up faster because of less rotational mass. The clutch is designed to withstand more power produced from the engine to allow a better engagement to the transmission. You only need these when you add over 100 hp to your car or more. The stock clutch will burn up faster because it will be more difficult for it to grip the flywheel when it spins and that causes bad launches and slipping between the flywheel and transmission input shaft speeds. Cons are that your clutch may be heavier and more difficult to modulate, and there may also be chatter when you engage and disengage your clutch, which is nothing to worry about unless it is loud, which can mean it was installed poorly. Also, you may stall out more frequently while you get accustomed to it.