If you need to serve a domain name or several domain names that point to a Web site hosted on another server:
Leave the www check box selected if you wish to allow users to access the site by a common and habitual URL like www.your-domain.com. Having the www alias preceding the domain name will allow users to get to the site no matter what they type in their browsers: www.your-domain.com and your-domain.com will both point to the site.
Bear in mind that e-commerce sites need a dedicated IP address (not shared among other sites) to implement Secure Sockets Layer data encryption.
With standard forwarding, a user is redirected to the site and the actual site's URL is shown in the user's browser, so the user always knows that he or she is redirected to another URL. With frame forwarding, a user is redirected to the site without knowing that the site actually resides at another location, therefore, Frame forwarding should be preferred.