This is a terrific read that gets to the heart of why progressive enhancement is such a solid methodology: progressive enhancement improves resilience.
Meeting our many users’ needs is number one on our list of design principles. We can’t know every different setup a person might use while building our systems, but we can build them in a way that gives all of our users the greatest chance of success. Progressive enhancement lets us do this.
The article is full of great insights from a very large-scale web project.