Nofollow tags are important in SEO, but I find many marketers I speak to haven't heard of the approach.
That's understandable since you would only expect SEO specialists to be aware of them. However, I think they are a useful concept to understand as a "hands-on" marketer, since they will effect conversations you have about buying media or understanding the way links in social media work.
Nofollow tags explained
A nofollow tag is a basic piece of HTML. Appended to a hyperlink, it allows webmasters to control whether search engines follow a link or not.
For example, the following URL on a page of another site allows search engines to visit Smart Insights’ website and credit the website with the link; each link is scored by the search engines, supporting SEO:
“In general, we don't follow them. This means that Google does not transfer PageRank or anchor text across these links. Essentially, using nofollow causes us to drop the target links from our overall graph of the web. However, the target pages may still appear in our index if other sites link to them without usingnofollow, or if the URLs are submitted to Google in a Sitemap. Also, it's important to note that other search engines may handle nofollow in slightly different ways.”
Three ways to use nofollow tags support SEO
Paying for adverts and/or links to your website. While you would obviously never do this to boost your SEO ;-), using a nofollow tag means you can pay for links on sites you believe will deliver quality traffic without running the risk of being penalised by search engines for buying links.
Link to competitors without supporting their SEO. Although you won't want to link to direct competitors, you may sometimes have to link to SEO competitors.
Forcing indexing and crawl prioritisation of your own website. Nofollow tags can be used to ensure search engines prioritise links to your important content rather than to generic power pages, such as Sitemap, Contact Us and Registration. This use of nofollow tags, sometimes known as "page rank sculpting" is most relevant to large websites.
Tactical SEO considerations from marketing campaigns
These are other implications of nofollow which may affect your campaigns.
When an agency adds comments to blogs, forums or social media, these will generally be nofollowed, so there is no SEO benefit. This is true for most links on Facebook, Twitter and LinkedIn.
Links in blog post articles are "dofollowed" so do support SEO and make guest posting a popular SEO activity.
Links are not always about the ‘credit’. Wikipedia includes nofollow tags in all its eternal links but still receives a lot of traffic. Relevant links are still effective in traffic generation despite the inclusion of nofollow tags.
Nofollow tagged social network links are still of great SEO value
Despite the fact that popular social networks include nofollow tags in most of their external links, social networks still have an important role to play in SEO; as well their contribution to other key aspects of digital marketing strategy, such as consumer engagement.
Links from social networks help to establish your brand is active and well shared.
Links from social networks help to build your ‘Social score’ - a key to SEO success.