When would this be useful? If your site has a blog with public commenting turned on, links within those comments could pass your reputation to pages that you may not be comfortable vouching for. Blog comment areas on pages are highly susceptible to comment spam. Nofollowing these user-added links ensures that you're not giving your page's hard-earned reputation to a spammy site.
Display advertising - As the term infers, Online Display Advertisement deals with showcasing promotional messages or ideas to the consumer on the internet. This includes a wide range of advertisements like advertising blogs, networks, interstitial ads, contextual data, ads on the search engines, classified or dynamic advertisement etc. The method can target specific audience tuning in from different types of locals to view a particular advertisement, the variations can be found as the most productive element of this method. https://www.pinterest.com/LibertyMarketing/