depends on what you want the end result to be. I just painted my Cuda last summer and I painted my car assembled. It can be done either way but if you want it like the factory did it or without any flaws, generally you have to at least have the doors, hood, trunk and front and rear valances off. I had the valances off but doors and trunk lid on. I didn't have the hood on because it is an AAR hood and painted it black. Most cars painted at a professional body shop will be painted assembled unless there is a color change and the owner is particular.
Many guys prime everything while it is disassembled, then before painting the color they will paint the door jams, under the hood, inside of the doors as well as the jam area on the doors and in the trunk. Then they assemble the car and paint the entire outside of the car. The reason here is so that any over spray (and you will have some no matter what) is body color.
