We’re all familiar with the concept of using the nofollow tag for external links, but there aren’t too many people who actually use it for internal links. The main reasons you should use the tag for internal links is because it can reduce duplicate content as well as control what pages you are giving more weight to. You only have so much juice that you can spread throughout your site, so why not spread it to the pages that count instead of wasting it on useless pages. Here are some of the things I like to nofollow internally:
Terms of Service
Comment RSS feeds
Duplicate navigation items (the ones that are getting linked 2 or more times from a page)
The nofollow attribute is just a mechanism that gives webmasters the ability to modify PageRank flow at link-level granularity. Plenty of other mechanisms would also work (e.g. a link through a page that is robot.txt’ed out), but nofollow on individual links is simpler for some folks to use. There’s no stigma to using nofollow, even on your own internal links; for Google, nofollow’ed links are dropped out of our link graph; we don’t even use such links for discovery. By the way, the nofollow meta tag does that same thing, but at a page level.
I know my advice on using the nofollow tag on internal links may be a bit basic and has been beaten to death, but it seems many people still don’t get why you should use them. Other than stopping useless pages on your site from getting too much juice, you can also control which of your content gets index. Yes content is king, but if you have a low PR site and thousands of pages of content, you may notice that you are getting very little search love. My removing (through the nofollow tag) the less worthy content on your website, you usually can get a decent boost in search traffic. This is especially effective if you have a PR 4 or lower site with over 1000 pages of content.
Have any of you tried using the nofollow tag on internal links? If so what type of results did you notice?