Link building is a good way of driving new people to your website. Not only that, but as you build more links to your website then the top search engines have more chance of finding your website without you having to add yourself to them. Link building is a vital part of SEO
How the top Search engines work
The best search engines work by following links either through your own website so that they can map it out and index your pages or by following links from another website to your own.