Why? Well, sometimes it might be relevant to see where in the world you were when you published a post, especially if you’re doing a travel-focused blog.
However, do you really want people to know where you are? Tabloids in Sweden ran a story on burglars using blogs to find out who was on vacation, and then broke into their houses. While that might happen for sure, I believe this particular story was a way to scare people into buying issues, reading about those scary blog things.
That being said, being at least a bit anonymous is what a lot of people find appealing with blogs.
Would you consider geotagging your blog posts?