The spectrum of commonly disabled browser features

Images enabled?	CSS enabled?	JS enabled?	Use case
Y	Y	Y	The full web. The happy path. The zen garden. 95% of people will see some form of this. However, progressive enhancement, natural browser variations, and adaptive/responsive design means that you can’t (and shouldn’t) treat this 95% as a monolithic block of pixel-perfection. It’s a sub-spectrum of features.
Y	Y	N	JavaScript is disabled. Common reasons for this: You are in a corporate environment that does not allow untrusted scripts to run You have got sick of dynamic web pages, and want a more peaceful web environment Your bandwidth is metered, or your connection speed is slow, and you don’t want to download lots of scripts that probably aren’t designed to enhance your reading experience. A script has crashed somewhere on the page, taking everything else down along with it. There are plenty of other reasons, but a lack of JavaScript does not imply that the user is working with a screen reader, or some other form of assistive technology. Screen readers do actually handle JavaScript these days. This is definitely a use case you should care about. As Mark Pilgrim points out, “If your web application fails in browsers with scripting disabled, Jakob Nielsen’s dog will come to your house and shit on your carpet.”
Y	N	Y	CSS is disabled, but JavaScript is enabled. You’re a web developer.
Y	N	N	CSS and JavaScript are both disabled, but you can still see images. You’re a web developer trying to figure out why your print stylesheet doesn’t work.
N	Y	Y	Images are disabled. This is actually more common and more useful than you might think, especially in low-bandwidth or expensive bandwidth situations. Most modern web pages still work just fine without images, they’re just a little less visually interesting. You should try it some time. Opera is the only browser that has consistently made it easy to toggle image downloading from a menu or keyboard shortcut. Other browsers allow you to do this, but you have to dive into their options or preferences screen, or install an add-on.
N	Y	N	Images and JavaScript are disabled, but CSS is still turned on. You’re trying to save ink while printing a web page.
N	N	Y	Images and CSS are disabled, but JavaScript still works. You are a client-side unit testing framework.
N	N	N	Free-range organic HTML, rendered as nature intended it. You’re an awesome time-travelling hard-core Unix geek from the Dark Days before Mosaic (aka 1992), or, more disappointingly, a bot. Hello, bot. Nice bot. Have a cookie.