In Firefox, if you click the hamburger menu and select "Customize...", one of the things you can drag into either the menu or the button bar is an RSS feed indicator/subscribe button.
You wouldn't believe how much it matters what the default is; people don't customize any more.
What I mean is that it is often used as a transport format for when some component or app will need dynamic and styled text content that update over time. Often in web applications, but not always.