Sheet music is incredibly important if you are working with musicians that can READ the page. I am classical trained musician but I also have been blessed to play by ear as well. I must say I hated getting whacked on the fingers with a ruler if I didn't play exactlly what was on the paper! LOL! I would say that as far as music in the last 50 to 60 years, the ability to write or read has greatly diminished. I heard Paul McCartney telling storys about him sitting and humming orchestra parts to George Martin while he wrote them out for the players to read in the sessions. Sheet music is the quickest way to convey your music to trained musicians. Sheet music also serves the purpose of you being able to leave behind a concrete, solid record of your work. As stated before it is not a requirement to be successful in the music business, but depending on the type of music you write it is a must as far as communication with READING musicians. None of these comments are meant to belittle anyone that doesn't read or write music. It's just a point of view from someone who does. I use a notation software to relegate my ideas to paper as a documented record so when I am gone my kids and grandkids can pull out my music and see what I did way back when. Who knows, someone may be able to actually perform my songs as they were intended to be heard, note for note, with all the expression marks to show the players the emotion intended in a certain passage.
Don't get me wrong in this post. I spent most of my teen years picking up and setting the needle back on the record player learning Hendrix, Clapton, Beck, and Page licks on my guitar! I have probably made more money playing pieces by ear than I ever would have reading the page. I wish you luck whichever way you decide to go. JUST MAKE SOME MUSIC!