Instead of relying on users to browse to the page and look for new content, RSS uses a feed of links, called an RSS Feed to identify when new content has been added to a web-site.
This allows a new breed of slim-line web browser called a News Reader. A great example is shown in the picture. NewsFire is a brilliant little application that allows users to subscribe to RSS Feeds and to continuously track when new stories become available.
For web-sites like Slashdot and Digg, which are used by many people, and have fairly unpredictable posting frequencies, a news reader allows you to read the stories when they appear, rather than fruitlessly rescanning Slashdot every 5 minutes, like some of … errrr, scratch that!!