If you are looking to build your readership, you want Google and other search engines to be able to find your blog. If you check your stats, readers that find you through search engines are a source of your traffic. They are a special source. They are full of potentially new readers to your blog, and therefore, they are key to growing your readership.
It doesn’t have to be Google, mind you. Even search engines that your blogging platform can’t recognize will show up in your stats as “unknown”.
Since search engines are looking for content, why not make yours easy to find for potentially new readers?