Why Should You Learn Music Theory?

Here is a small list of things that music theory will help you with:

Understanding why your favorite musician used a certain chord in his or her song.
Writing your own songs.
Making nice sounding chord progressions.
Becoming better at guitar, piano, or any instrument you play.
Understanding why music makes you feel certain emotions.
Writing songs that are incredibly beautiful, catchy, happy, sad, and everything in between.
Filling in the different sections of a song.
Helping you get past writer's block when you are stuck and can't think of what to do next.
Understanding what notes to use when you play a melody over a chord progression.