You might want to have more than one Web site if you want to give different Web portal users access to different information. Then you could divide the information on separate sites and grant each user access to the appropriate site or sites. For example, you might have one site for wholesale customers and another for retail customers.
Or you might want more than one site so you can build up a new site while the old one is still in use.
Web Site Setup
Importing Template Properties
Copying a Web Site