CSS allows website designers to truly customize a web site and to do it easily. CSS allows the web site designer to more easily control all aspects of presentation and reduces the amount of bandwidth needed for, and size of, a web site.
CSS requires only one style sheet instructing the print parameters of a page instead of having to code each page individually.
Using CSS allows website owners to use the content of their site more easily as the HTML coding that would be needed to create the visual aspects of the page. This is useful for programs that translate text into speech or for putting the content into a feed.
CSS has many different functions and is one of the most useful and important tools in a web designers toolbox.