It's actually harder to get a good finish with spray. The viscosity has to be very low and it takes a lot of experience. To build up coats as you do in varnishing to get a deep gloss will take you forever where as auto body work is with color that doesn't need a build up. You need exhaust fans and dust freee area etc. and it's easy to get orange peel from over spray unless the viscosity and spray pressure is just right. I do paddles with Minwax spar varnish in a spray can. It's so easy to get a run. And if you don't lay on enough, you got orange peel.