Please allow me to disagree slightly with your assertion. While nofollow links will not be included in Google’s link graph, you go too far asserting that “no-follow links will never help you in getting ranking.” “No, follow links only helps you in getting traffic.”
True, there is no direct benefit, however, there can be a very positive indirect benefit. If you create highly useful content you still have a problem of getting that content discovered by users of the Worldwide Web. As you said, Nofollow links can be useful for generating traffic, which when combined with quality useful content will lead to natural backlinks, the kind that search engines value the most.
wow no-follow links really work useful content + human traffic = natural backlinks + higher SERP rankings
