I use the air brush tool in just about everything I do. Anything that requires a customizeable soft edge or smooth transition needs the air brush — and not just for applying color to something. If you want to apply a layer mask (to hide an object) or a layer effect (that changes either an object’s color, tint, or sharpness), you would use the air brush. If you want to make special objects like stars, or apply a custom pattern in different levels of opacity, you would also use an air brush.
If you have an educational license, I would estimate you’ve spend about $3000 over the last decade in subscription fees. You better get to work.