I'm not a painter by trade and do only my smaller stuff and will eventually do my car. Maybe that's why I understand the point of using single stage on the engine compartment - and also the underside, interior, small parts, etc.. The advantage is that with very little effort you get a nice glossy finish that requires no wet sanding and buffing. Just imagine doing an engine compartment in base clear, wet sanding and then trying to buff the thing !!