Hello
It is possible to paint a element so good so it does not need polishing? My car painter always do a polish after painting. I curious if it is possible to put paint without need for polishing.
Yes! But it depends on what you are expecting of the finish and what type of paint you are working with.
If you are looking for a paint finish with texture and gloss to match the original finish, then it is absolutely possible. But if you are looking for an absolutely flat, best-in-show finish, then the answer is no.
Differing from Mike, I have never seen any "as sprayed" finish "flat-as-glass". The only exception may be convex curves where the shape tends to conceal the texture.
Today's urethane clear-coats, along with most of the enamels of the past, do not require sanding/polishing to achieve an original equipment look. They can be sprayed and done. They do not require polishing to achieve their gloss. But they will have some texture to them, similar to an original equipment paint finish. Lacquers from the past always require polishing, at a minimum, to achieve a high gloss.
I think the most common reason today that body shops sand and polish a new finish is to remove any dust nibs and the like. I don't care how clean you are in your processes, a 100% dust-free finish is nearly impossible... Even factory finishes have a few minor dust nibs here and there most of the time.
I do agree with Mike that after the paint is fully cured, that sanding and/or polishing will make it look better... But I'll also state that is not always desired. When repainting a portion of a vehicle, you don't want to sand and polish the paint to the point that it looks better than the rest of the car. Your main goal is to make it look just like the rest of the car, like it was never repainted.
In most cases of high-quality work with today's finishes, that goal is best realized in the "as sprayed" or only "lightly polished" condition.