As mentioned, RSS is used by RSS readers to keep tabs on constantly updating content.
Typically this would be something like: today’s sports/business stories, every single weather watch issued by the National Weather Service, or the last 10 blog posts on Daring Fireball.
Like most XML-based formats from the early 2000’s, it’s complex, excessively verbose, and hard to read as a human (hello CDATA) but it’s good enough for computers.
What killed it was Google killing off the most popular reader (Google Reader). They did this mostly because people wouldn’t go to the destination websites… which is bad for their pagview metrics.
Ultimately Facebook came along and put everything behind their wall, where no RSS feeds are available.
git stash, girl