I get asked this question all the time. "Why do I need to read music?"
Well, imagine if you couldn't read English. First, you wouldn't be reading this post. Imagine if someone had to read everything to you everyday, from street signs to magazines, to text messages and Facebook status updates. How would that be for you? In a word, debilitating.
Certainly there are lots of good people in the world - brilliant, even - that can't read or write. But those people, almost without exception, would encourage you not to follow their path. Reading and writing are the gateway to learning and communication on a much higher and more efficient level.
The same is true for music. Of course, there is much to be learned from listening and imitating. And there are many great musicians who never learned to read or write music. But the written version of what you're hearing can allow you to be more expressive and accurate than you could ever be without seeing it. Written music also fills in more of the "why" of the music, sort of like how books can tell you a character's thoughts, but the movie rarely can.
For my money, reading music is as critical to the musician as reading and writing your spoken language is to the average human being. Not doing it won't end your career, but gaining the skill can only make you better.