Associating Domains With Sites
Whether you are using the default Central domain or host mapped domains (or both), any of the sites that you create can be associated with any of the domains on the URLs page view
Example You are producing some knowledge bases and several online Help systems for your company, FictionSoft.
Perhaps you want all of the knowledge bases to point to kb.fictionsoft.net, and you want the online Help systems to point to help.fictionsoft.net.
Therefore, you can add those two host mapped domains to the URLs page view. Then, when you create a site, you can point to one of those two domains, depending on whether the output is a knowledge base or a Help system.