Video : How To: Multisites vs. Multiple Sites

Using multiple domains with Drupal

If you have multiple domains, all going to the same website, you can redirect traffic to your 'primary' or 'default' domain instead of serving the same content on all domains. Google measures your websites authority over the number of links to you website, if you have several domains, some using www. some not, then that authority is spread across all those (sub-)domains.

Tutorial : Configuring Drupal Multi-Site to handle Muliple Domains from One Drupal Installation on Dreamhost