Link building has a threefold purpose for SEO. Links measure popularity, increase 'link juice' and social media visibility.
Simple example, if you are a popular Stock Analyst and post a blog of your stock picks, other Analysts will link your stock picks as reference to the choices they made. Since so many Analysts link to your content, Google makes the assumption you must know what your talking about. Hence, your blog rises in search engine results for the keywords you've chosen to emphasize in your content. Bottom line, Google wants to get the best answer or most authoritative result to a searcher. Links used in this way are referred to as 'contextual links'. Contextual links have a keyword associated with it and are used for both external (inbound) and internal links. The inbound links to your web site have a keyword associated with it on the referrer web site. In other words, the link referring to your text comes inbound to your web site.
The second use of link building is creating 'link juice'. As you read through this text you will see references of keywords to definitions. The references are contextual links. The contextual links are placed strategically on keywords with the assumption the reader may need further understanding of the subject matter. The second reason is to create link juice. A 'spider' will craw the text and travel the link to other parts of the web site. Without the link, the spider may not crawl the entire site, not knowing a way to get there.
Lastly, a third type of linking has grown in importance. Having web site content shared 'linked' on social networks. Linking to social networks has various benefits. Those who view the shared link have several options to 'vote' for it's popularity. Votes come in the form of 'likes', shares or tweets. Google has placed heavier consideration on links shared or 'liked' on a social networks.
What's really nice about sharing content on social networks, the internet visibility is instantaneous. You don't have to wait for your content to be indexed by the search engines and then the timely process of internet users catching on to the importance of your text. If you have a social network of a few thousand people, by posting content you get instant internet visibility or 'impressions'.
'...special advanced tools that extract or 'scrape' the internet to see not only your inbound links but your competitors too'
e<Meta>Star, LLC has special advanced tools that extract or 'scrape' the internet to see not only your inbound links but your competitors too. We examine all types of metrics telling us the strengths of the inbound links and how that correlates to search engine results on your chosen keywords. An inbound marketing campaign isn't about quantity but quality. What quality links are going to lift up your content to greater internet visibility.