What is no follow?
For a HTML hyperlink tag it is a value assigned to the rel attribute.
For example:
The output of the link looks like just a normal hyperlink:
The only difference is that it doesn’t sends any vote to the linked URL. In other words, it’s as good as telling the search engines that hey, thats just a link, but I am not saying that I like this site or anything like that.
What’s the purpose?
Search engines don’t like pages passing Page Rank and vote to other sites when they are not relevant. By using this value you don’t pass any votes to any external sites.
Hows that useful for your blog?
When you don’t pass any vote that means you are telling search engines that you are not a guy who’s here to sell links and tamper with the philosophy of search engines. Your just a guy who’s here to blog. As a result, your blog will rank better in search engines and it would become credible.
But, why to make it nofollow for all the external links?
Why not? Since you are not selling any links on your blog and you don’t wish to sell in near future then what difference does it makes anyways. You are just playing it safe. What’s wrong in that?
Wait, I have a blog running from almost 3 years? What am I suppose to do now? Do i have change every link manually?
In that case you should download and install this plugin. It automatically converts all your external links to nofollow. Also, it adds another attribute to all your external links: target=_blank which means when someone clicks an external link it would be opened in a new window. This plugin will not tamper any of your internal links. The only drawback of this plugin is that you can’t change any external link not be nofollow or not to be opened in a new window. There are no such settings in the plugin. But I guess it is not required also. It doesn’t matter that much if they open in a new window.