The process of getting a link to your website on other websites of relevance and importance is a central part of search engine optimisation. If you do this right, then you will see an increase in quality traffic by having a qualified and relevant stream of people visiting your site due to your inbound links.
Also, the number of sites that link to yours is an important factor for search engines when they decide how relevant your site is in relation to a particular search term. Search engines have even begun recognising whether the link is from an important, relevant and successful site or just your mate’s blog so as you can see, inbound links are key to your SEO success.