I was watching a youtube video on repairing paint chips and the guy said 'if you cant see rust you don't need primer.
However I notice that plastic(which doesn't develop rust) has primer layer on it. Therefore if you were painting damaged plastic body panels you would need primer and even if paint chips, the primer on the plastic may have become too thin from damage.
So seems to me his advise is incorrect? Please explain.
Since the video was about smapp paint chips, maybe he was saying in the case of those its not needed?