Many times I have conversations with people who don't blog and some of whom don't get blogging at all. I usually find these conversations a little awkward, because by and large blogging is a different type of conversation and I find 'as I said in my blog' a sentence which annoys people and a conversation which begins 'I read in your blog' annoys me because I would rather they commented and had a blog-discussion than a real one. Real conversations start in a different way, I find.
But if you want to know about the usefulness of blogging follow this link from the BBC to an article explaining how bloggers get at the truth in a way nobody else can.
You are an expert in your little bit of the world and at whatever it is you know about it. Regular readers of this blog know a lot about, inter alia, horn playing, complex mathematics, university chaplaincy, computer programming, Portsmouth FC, teaching unteachable kids and their own very local geography.
You may be able to solve an international problem just because you are who you are and you have a public forum.