Aristotle would have been proud of this blog post. Mario Sundar lists the different types of blogs you can start. Think this is arbitrary ramblings? Go ahead and try it. Almost any blog you can think of fits into one of these categories. Albeit the industry blog or the CEO blog.
I think these categories have a special importance when you come to look at objectives. Here you can see how you can have a very broad set of objectives for each type of blog and still not overlap.
The other useful thing about categorization is that it supports the notion of having multiple blogs. There are different avenues for you to go down if you have the energy.