>>23497234
You need to shake paint bottles to mix the pigments with the medium. Paint naturally separates over time, so it can end up being too thin, forcing you to do multiple uneven coats, or too thick and chalky(pic related). Shaking the bottles by hand is tiring and doesn’t always mix the paint well, which is why people use vibrators to mix paint evenly in the bottle.
Not to mention that poorly mixed paint can splatter in an airbrush or even clog it completely.