Do follow Back links is the most powerful way to influence search engines to redirect a lot of traffic to your site. Search engine crawlers crawl the whole content on your webpage including images, links, keywords etc.
No follow links can be relevant to your post’s content and can come from the sources which have a potential to generate high referral traffic.The site is crawled but not indexed in search engines index. While it's a no follow link you cannot get the link juice.