Technology is always in motion, this is also true for webbrowsers. These developments result in ever increasing oppertunities in web design.
Every time a browser gets updated, new features get added. The more browsers support a certain feature, the safer it gets to use this feature. If you use one of these newer features there is a risk that something goes wrong on browsers that don't support this feature (yet).
Sadly, many people still use old versions of their browser. That's where 'Graceful Degradation' comes in play. This means that we use the newest techniques available in modern browsers, but provide alternatives for older browsers (i.e. Internet Explorer 9 or older).
By doing this we can be forward thinking with our sites, and guarantee that it will be functional on all computers.
Read more about Graceful Degradation