Am in the process of getting a '66 Fastback painted, and one of the guys bidding on the job talked about "shimming" the doors, fenders, hood and rear lid. I guess he paints the door jambs and openings with the parts off, then mounts everything up but shims it out away from the frame, and shoots the exterior

.
Being a newbie I'm still learning about this stuff, but I would have thought you would get a better job by painting the parts off the car. Yes?? No?? The guy has been painting cars for better than twenty years and comes recommended....I guess my problem is I was expecting something different, but hey, I don't paint cars.
Any feedback greatly appreciated!
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The Universal Truths in My World:
1. There is always month left at the end of the money.
2. Fish always bite the other guy's hook.
3. Not even my wife will interrupt surgery on a pony.
1965 A-Code Fastback
1966 RestoMod Fastback, 5.0L