Shimming of all body panels and even bodies has been going on since the first car was hand built. (same can be said for home building). Ever time I disassemble a vehicle, I collect all the shims right along with nuts, bolts and special fasteners, for future use. When I retired and started building/restoring vehicles with my Bud, door, hood and panel alignment intrigued me a bit. My Bud, a retired master tool and die maker, had a great eye for determining what had to be done to make those perfect lines and at first, I always thought he was going in the wrong direction, but I soon learned that he was always right. Hard to learn that up is down and left is right!!