Websites with higher authority are shown higher in the search engine results and receive more high quality visitors for their most important keywords.
The search engines determine your website’s authority based on its reputation on a variety of topics. Several factors can increase your website’s reputation for any given topic.
One factor is the number of properly optimized pages on your website about that topic. But a much more valuable factor is the number of other websites (about similar topics) that contain links back to your website.
Because of this, trading content for incoming links from similar websites, and producing content on the right topics on your own website, are the two most effective activities you can do to increase your website’s authority and thus increase the number of high quality visitors your website receives every day.