I know of way too many people that think plugging things into an app or clicking a button in Photoshop is design. Don't get me wrong, these things are handy and cool but it doesn't make you a designer.
Your designs can spark a whole range of emotions in people. Color theory unlocks the secrets of how to use hues to inspire joy, sadness, and even hunger. -- or, you know, make art or not to have clashing colors.