Link building is an important part of any SEO campaign. It can be a little tricky. You need to be careful.
The first reason link building is important is that it helps Google discover content. The Google search engine spider crawls the web to find content to serve in the search results. How does it discover content to even consider for its index? Through links to different pages.
The second reason link building is important is because of the way it evaluates the pages it discovers. Ever since Google was launched in 1997, it used a fundamentally different way of evaluating web pages. While it considered the content on the page, it used links from other sites to determine which page was better than the others.
Links determine what webpage is best like this (taken from a Udacity course about building a search engine):
There are hundreds of ranking factors behind how Google decides to rank a webpage. Some are more important than others. Since links are fundamentally behind how Google was originally built, I’d suggest it is still important for better ranking a page.
It’s so important to Google that, once people learn about link building, they tend to go a little crazy. As a result, Google has set rules for what is fair, when it comes to link building. Before you start any link building efforts, be sure you’re familiar with these rules. If you break them you might find your entire site banned from all Google searches.
If you read them you might ask yourself, “Does Google allow any link building at all?” These guidelines seem to discourage link building in any form. That’s where this becomes tricky: to show up and rank in Google, we need links; however, Google forbids many forms of link building. To put it another way: we’d be negligent if we build links and negligent if we don’t.
Eric Ward was the most respected link builder I’ve ever known, His answer to this was: would you build this link even if Google didn’t exist? In other words: we don’t build links just to improve our ranking in Google, we build them because they help people. If you take this philosophy to link building, you won’t run into trouble.
Links to a site establish that other websites think your site is an expert. Our goal is more and higher quality links. Sure, some of these might send traffic. to your page. In fact, links that send traffic tend to be better than those that don’t. However, the traffic is gravy compared to the increased credibility your site gets, in Google’s eyes, from the link. You’ll get more traffic from Google search, due to better ranking from links, than most links will send you themselves.
For example, I once helped a client get a placement in his industry’s most respected periodical. If we measured success of this link by the traffic (and/or conversions) we would have judged it a failure. However, as Google gave this site credit for the link, we started to see more and more organic traffic to the entire site. This was a result of the site getting more authority and each page ranking better.