I believe every piece of writing reflects the author in some way. Perhaps not in the sense of a direct, literal transfer of an experience or event, but rather as the residue that these experiences and encounters leave in a writer's soul that eventually emerges as a story.
It gave my writing substance because I was then addressing an audience, and that's very different than when, for example, you talk to yourself in front of the mirror. It became communication, and as such it had to be authentic, well-researched (especially in my chosen genre of historical fiction), and meaningful. Publishing my work made me more responsible about what I put on the page. There has to be a message that needs to be conveyed, one that I feel other people might want to or should know about.
I was in my teens when I started writing my first stories. I'm not sure exactly what it was that drove me there - it was like the characters in those first stories spoke to me and compelled me to bring them to the light. That's the mystical aspect of inspiration. I suppose the scientific rationale would be that I grew up rather lonely and, unconsciously, I was probably looking for an escape. Either way, writing made me feel happy. And it made me feel free. You get addicted to these emotions, don't you?