My roof was bare sandblasted metal, my quarters and fenders had the factory primer that new sheet metal comes with and my doors, hood and trunklid had $1400 worth of bodywork, primer and white sealer on them. There is NO difference in how the paint turns out. The primered parts looked like they covered better at first becaust the primer was white, but once you get about 4 coats on, there is no difference. Unless you are smoothing something out with a high build primer, don't waste the time. Spend 10 bucks on a package of 10 high density foam rollers, get the mineral spirits and a gallon of whatever color you want and go to town.