Drupal’s elegant multi-site capabilities give businesses a repeatable framework on which to run many websites from a single installation of Drupal—enabling centralized system management while reducing the incremental cost of additional websites to almost zero. The benefits of multi-site include streamlined maintenance, lower operational costs, and the ability to target market segments in a more controlled way.
To successfully implement a multi-site installation, a business must also be aware of caveats and changes that may be required to their deployment model. If you are looking for a cost effective way to manage multiple websites, Multisites are what you are looking for.