SEO is the only process that can make you visible in different search engines . In seo you have to do link building to get top and stable listing in various search engines. For inbound link or outbound link the “dofollow links” and “nofollow links” matter a lot. What is “dofollow link” and “nofollow link” ? Actually if you don’t use “nofollow links” that is “dofollow links”. Now what is “nofollow links” ? There are many links on your link page which you do not want to crawl by the search engine spiders .
It could be paid links or could be blog comment section which effects on your ranking. As “nofollow links” don’t followed by spideres so search engines in the time of giving page rank don’t calculate this. So in the time of link exchange taking “nofollow links” is waste of time. And “dofollow links” is the best.