When setting up a web site, it is important that the site is displayed properly in all screen resolutions. Even though very large screen resolutions are common nowadays, most people still use an 800x600 resolution. If your site doesn't display correctly in that mode, the visitor has to scroll to see your site. This is not only tacky and unprofessional, it can cause a loss of visitors since people don't like to have to work to view a site. That is where this change comes in at. It sets up the shop so that it views properly at any resolution, providing there isn't something that will override that like a very wide image. It also allows you to easily add colorful borders and backgrounds to your site.