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.
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.