Example: Let's assume you own 2 domain names (test.com and test2.com) and you'd like for each of them to include different content. The only problem is you're on a limited budget. If test.com is your primary account domain name and you'd like to use test2.com for a new site, you can add test2.com as a secondary domain name pointing to a subdirectory on your primary domain name, test.com. The secondary domain name, test2.com, can be added in a way that the visitor will be redirected to the subdirectory on your primary domain name without even knowing it. The URL in the browser will show up as "http://test2.com" instead of "http://test.com/subdirectory".