I still rattle can some things like primer and certain flakes, but a builder without access to an airbrush is a bit limited only to certain types of paint jobs. Graphics are very hard to do on a model without an airbrush, unless you just do decals all the time.
I don't know, I feel the airbrush offers a great deal more control and possibility to paint jobs. That's just my opinion, of course, I know builders who get lots of great results using the rattle can.