The purpose of a blog is different to everyone
Most of the time when I start writing a blog post on here, I have a very fuzzy image of the topic (or topics) that I want to discuss. But that's what's great about blogs — you're able to take an idea and roll with it.
There is no need for an outline, a rough draft, peer reviews, et cetera. The only thing needed is the determination to write and a keyboard. Of course, treating a blog post like an essay will result in higher-quality content. But there's no need to write such content — a blog is what you make of it.
It can be a journal of your daily life; a place to figure out complex feelings; a way to document an exciting discovery in a niche field; the possibilities are endless. With a blog, a person discovers that writing is not just a medium in which information can be exchanged — it is so much more. The artistic versatility that a blog provides is akin to a blank canvas.
Take some time to write for yourself once in a while. You may need it.