Creating sub-domains gives you the ability to create shortcuts to special files, folders or websites. Say for example that you’re working with a freelance client and you want to point them to a folder on your site where they can see their new redesign. You could tell them. Go to http://iviewsource.com/clients/clientname/projects/website/redesign which is tough to remember and long to even try and say over the phone. With a subdomain shortcut, you can simply tell them to go to http://clientname.iviewsource.com and the server will automatically redirect them to the same folder.
That can also be powerful when your redesign a site. Depending on how you set up your server, sub-domains have the power to act as real domains. So I often use a subdomain like http://staging.iviewsource.com for site redesigns. With most web hosts, you can put the redesign files in a folder and then simply redirect the main url to the new folder when your site is finessed…that way you don’t even have to move files from one “staging” server to a real server.
You can often create a sub-domain to a file or page, so you can do something like http://specials.iviewsource.com or http://summercamps.iviewsource.com. The possibilities are endless. Subdomains are a power-tool for web pros so if you haven’t tried, it’s something you should definitely check out at your Web Hosts.
Here’s a video from my series on Managing a Hosted Web Server that shows you how.