When designing a website with javascript, what is the need to test the website with javascript turned off? I've read this a few times, that a website should work when javascript is not available on the browser (for some reason). Who does this, on what percentage, and why?

I understand there are some security concerns, and tools like NoScript disable scripting... but you do expect dynamic sites to break if you cripple the browser, it's normal. Why would a javascript programmer worry about these corner cases?

Thank you