Blogger by default and so WordPress, automatically adds the "nofollow" microformat extension to all links from user generated content. User generated content is defined as comments or external sources such as linkbacks and trackbacks.
Whats the advantage of changing this?
It will influence the link target ranking in the search engine index, so whenever someone input their URL address in URL form their site ranking will automatically increased but only if the site they put the URL have high Rank. If the Rank is 0 then their site can increased still in the search engine index but only a little
Now Whats the disadvantage?
We have discussing about the advantage, now whats' the disadvantage? Since its enabled, there is a chance that spamming attempt will increased on your site so you'd better to monitor and always keep an eyes of those spammer
1. Go to your Dashboard Layout, click on Edit HTML and check on "Expand widget Templates" box
2. Find the nofollow attributes by press and hold down CTRL follow by F (CTRL + F) and find these line rel="nofollow"
3. Remove the code once you found it, keep searching they could be more than one. Make sure you have backup your template before you are doing it.