Music Theory is the study of the practices of music and the possibilities of music. It can also relate to concepts, belief systems, silence, musicology, psychology, mathematics, time & space. Music theory is forever evolving, its base is in these 4 principles: Pitch, Rhythm, Harmony and Structure. If you want to further your career you have to understand these 4 basic principles. Becoming a musician and/or a producer isn’t just simply finding a sample and laying a few bars on top. Studying the theory of music will set apart the true musicians and/or producers from the posers. If you have only used samples when creating music then understand this is just your hobby. There is nothing wrong with that, everyone needs a hobby. However, if you want to make it in the music industry educate your self and learn your craft, because we can hear it in the music.