Writing as Therapy?

I kept a diary when I was young. From age nine to twenty-one I wrote in those cherished journals most everyday. Sometimes the entries were mechanical and boring, other times quite insightful and interesting. The most fun has been digging them out of the cedar chest and reminiscing. What is most curious to me -- and it's not exactly possible to go back and ask myself -- is why? What gave me incentive to keep a diary? Was it trendy? Was it because of loneliness? (I was an only child.) Was it my way of thinking and talking about my feelings... what bothered me, what excited me, made me sad, angry, happy? And then later in life, as my writing expanded to short stories, song lyrics, and eventually novels, has that writing been for the same reasons? All I know is that writing became a part of my life, a very important part. A way of expressing myself. But is it or could this practice be labeled therapeutic? I think so. I've given it much thought. And that's my conclusion. Maybe it doesn't matter. Maybe it shouldn't matter, as long as it makes me happy. However, it's interesting to consider the "healing" power of writing. What do you think? Is writing more than the creative, informative, entertaining art form we enjoy? Is it therapeutic?