Some paint questions for the guys who know paint

I have always gone by the old school painting methods and I have color sanded metallic paints before with no problem.....the old method of misting your metallics in the gloss coat to keep it evenly distributed in case of any mistakes. Why do you say urethane over enamel? enamel has more of an eggshell finish too it and is what was used back when. not trying to second guess you here.....I am just saying that I havnt had any problems painting the old school way.