I think for getting the best paint job, there is no avoiding using a little bit of very fine sand paper (or piece of sanding sponge) to both smooth a slightly uneven painted surface (because of primer, paint or even a gloss coat). When using an airbrush, one might easily end up with some kind of splatter which can easily be removed, as long as one is careful not sanding through the layer of paint or primer. Obviously sanding on top of a thin layer of paint is risky, and is predictably destructive when trying to sand anywhere near an edge, because of the extra and unintended pressure there when all the weight ends up on a very thin edge, easily sanding though primer and paint. Sanding a layer of paint should be easily fixed if also adding a gloss coat on top, then, the "scratched" black, looks the same as the rest of the black after a layer of gloss coat. I am still not 100% comfortable using a gloss coat, and apparently some people don't even rely on adding a gloss coat.
1. May, 14:33