Should a blog have a purpose?

It occurred to me today that I blog without purpose. Most bloggers have some form of thematic category that they blog about in general. I on the other hand don't.

My blog post are generally totally unrelated from one post to the next. It's more like a public accessible diary for me.

Most blogs what have related posts ted to be the more popular ones. Where as I am not to bothered about having an array of followers. I just blog because I like to write occasionally.