In an effort to manually control the flow of PageRank among pages within a website, many webmasters practice what is known as PageRank Sculpting—which is the act of strategically placing the nofollow attribute on certain internal links of a website in order to funnel PageRank towards those pages the webmaster deemed most important. This tactic has been used since the inception of the nofollow attribute, but may no longer be effective since Google announced that blocking PageRank transfer with nofollow does not redirect that PageRank to other links.
PageRank sculpting came out of the idea that virtually any page will have links that are important for users but not necessarily that meaningful to receive any PageRank that a page can flow. Navigational links are a primary example of this. Go to a place like the LA Times, and you’ve got tons of navigational links on every page. Nofollow those, and you (supposedly in the past) ensure that the remaining links (say your major stories) get more of a boost.
Social media is a mixed bag when it comes to backlinks. There is a modicum of value, as social media sites allow you to link to your website in your profile. However, these days Facebook, Twitter, and other social media sites mark links as 'nofollow,' meaning that they don't pass SEO value (sometimes referred to as "link juice") to the linked site. These links won't do anything to boost your site's performance in search results.
Yes, the more links on a page the smaller the amount of page rank it can pass on to each, but that was as it was before. With regard to what happens to the ‘missing’ page rank, it seems that if this is the case all over the Internet, and it will be, the total amount of page rank flow is reduced the same all over so you don’t need as much page rank flow to your good links to maintain relative position.
On a blog the page rank should go to the main article pages. Now it just gets “evaporated” if you use “nofollow” or scattered to all the far flung nooks and crannys which means google will not be able to see the wood for the trees. The vast majority of a site’s overall page rank will now reside in the long tail of useless pages such as commentors profile pages. This can only make it harder for google to serve up the most relevant pages.
Search engine optimization is a key part of online marketing because search is one of the primary ways that users navigate the web. In 2014, over 2.5 trillion searches were conducted worldwide across search engines such as Google, Bing, Yahoo, Baidu, and Yandex. For most websites, traffic that comes from search engines (known as "natural" or "organic" traffic) accounts for a large portion of their total traffic.