Well. with all the panels on the car in my opinion you can never get as clean a finish painting everything together. Painting separate you can get into every corner and put a slick finish on every panel. wet sanding and buffing is much easier doing every panel separate. I will also back tape the painted side of the panel after paint and finish the back side of the panel.No way to do that with the car together. Look at my Face book page and you will see in all the full builds we do this to every car to every panel We also buff all the door jambs, wet sand and buff will take me around 60 labor hours from start to finish.