There are two ways to content on the web. One is for you to visit a site and read the content there. The other is for the content to you.
RSS is what allows the latter to happen. With a service like Google Reader, you can stay current with all the sites you like without having to wait for any of them to download. All you have to do is submit the url for the feeds you want.
You can read more about RSS here, but the gist is that RSS feeds make it very easy to retrieve and process all the information and content you want very efficiently.