The main reason is to drive traffic to your site. When used correctly link trading can increase your number of visitors by the thousands. There are three main effects of having a lot of links out on the Internet pointing to your site.

1. People will see the link to your site and click on it while browsing through your link partner’s web sites.
   
   
2. Search engines will rank your site higher if you have high link popularity. Which means your site will show up on top and not on the bottom of the search results.
   
   
3. Many search engines use what is called "Spiders" to crawl the internet and index new and updated old web site. If your site does not exist in the google.com; for example that means that google.com they have not indexed your site yet. The "Spiders" will more easily and more often crawl your web site if a link to it is placed all over the Internet. Your site will be listed quicker and it will be revisited more often.