Get the paint wrong - easily strip it off and redo it. Get the powder wrong and its a whole different ballgame!

I my case and probably others as well, there is rust in the top corners which is not severe enough to cut out but enough to need a skim coat of bondo. This means powder is not an option as it won't adhere to the bondo. Also, doing an ashtray you only want the door done, not the tray itself. Unless you pop it apart and re-rivet it you're pretty much dinked there as well.