The "nofollow" attribute makes it so a link will not be indexed by search engines. It has to do with search engine optimization, and will make it so that particular <a> will not create a backlink for whichever site you are linking to. No follow tags have been criticized, because they don't really serve a purpose, other than making it harder for someone's site to be SEO'd well.
Mostly, the nofollow attribute is used to stop spam on the web page by blogger but except it, we can also use this tag for many situation such as : When linking to the same page many times from one page At the time of internal linking Paid links and ads Untrusted content
When I have a page that has multiple links to the same source, then that is when I use the nofollow tag.
If our website link in sample means, then we should use this no follow tag to link the sample. Then only it does not affect the PR
nofollow is a value that can be assigned to the rel attribute of an HTML a element to instruct some search engines that a hyperlink should not influence the link target's ranking in the search engine's index.example :- href="any site name " rel="nofollow" you should write in tag 'a'
Google announced in early 2005 that hyperlinks with rel="nofollow" would not influence the link target's PageRank. In addition, the Yahoo and Bing search engines also respect this attribute value.