When you get serious about making stuff you start to appreciate one trusty friend who's there for you throughout your crafting career- the aerosol can.
Aerosol spray covers quickly and easily, with minimal mess and practically no clean up, and nowadays many different mediums are available in spray cans, from chalkboard paint to water proof sealant.
But the most popular medium is spray paint, which is more convenient to use than brush-on paint, dries evenly and leaves no brush strokes, so your project has a uniform coat and a professional look.
So why use spray paint instead of a regular latex or acrylic paint out of the can?
It adheres to damn near everything you want to paint (they even have a spray paint for plastic that works like a charm), you rarely have to sand or prime the surface you're painting, and you can apply multiple coats without caking or flaking.