Painting question, should i paint parts separate or together...?

[pound41]

I have never done one this way. But I paid $6000 to have my 69 RS/SS Camaro by the guy who has painted the Oakley sunglasses funny car and hungreds of others. I think it come down to like rat said. Boxing your paint which means mixing multiple gallons to insure enough. Exact measurements of everything. Anyway they painted the body. The doors, hood etc painted off the car. Taped off door jamb where the 2 painted edges met in a seam. Sprayed and cleared it all. Let it sit for a while put it back together. Sanded with 2000grit. Buffed the whole car. Uniformed and glass. I am thinking of trying it on my blazer. I watched most of the work done on my camaro at night. All the others I have sprayed myself were with all the panels on the car.