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.
The term was first used by Internet theorist John Kilroy in a 2004 article on paid search marketing. Because the distinction is important (and because the word "organic" has many metaphorical uses) the term is now in widespread use within the search engine optimization and web marketing industry. As of July 2009, "organic search" is now common currency outside the specialist web marketing industry, even used frequently by Google (throughout the Google Analytics site, for instance).
Google says: “So with the mobile first indexing will index the the mobile version of the page. And on the mobile version of the page it can be that you have these kind of tabs and folders and things like that, which we will still treat as normal content on the page even. Even if it is hidden on the initial view.” Source: https://www.seroundtable.com/google-content-hidden-mobile-24111.html
There are several web traffic referral sources. Organic traffic comes from search engines. Referral traffic comes from other websites. Display traffic comes from ads for your business on other sites. Paid traffic comes from promotions via sites like AdWords. Social traffic comes from social media sites. Each type of traffic can be further divided into individual traffic sources. For example, organic traffic can come from Google, Bing, or other search engines. And social traffic can come from a variety of sites.