I draw because I can't visualize. I think in senses and in 'thoughts' or feelings. Rather than see something when I close my eyes and imagine, I just get the sensation of that thing being near me.
So art is my crutch. Art is how I enable myself to see what I imagine. Anyone can describe a scene, but I have to physically draw it to understand how it looks.
One of my friends, the only other person I know who can't visualize, is absolutely baffled that I can draw at all (he can barely manage a stick figure), while my brother says it helps me because he just gets frustrated that his art doesn't look how it's supposed to while he's doing it, and his inability to make hos art match his visualization is too discouraging to him... I don't know if it helps or hinders me, but it's what I live with so it's how I function.