on cars that are stick shift, light flywheels make them stall easier.
on mini bikes, drag racers like to use them because it helps accelerate faster
on go karts, some people dont like to use them because it helps the kart decelerate on turns, so it bogs down with less rotating mass, just like a car would when a load is applied when you are letting the clutch out.
accelerates/decelerates faster. Not necessarily a good thing unless you are into racing in a straight line and dont care about turns/shifting problems at low rpms.