Just writing knowing that someone might read it inspires better writing. It's like when you think about a problem really hard, come up with nothing, then spend an hour formulating a perfect StackExchange question. More often than not, the process of writing for other people leads me to the answer, even without sending the question.
Same with blogging, except I can publish any old crap on my blog without moderation.
Same with blogging, except I can publish any old crap on my blog without moderation.