XML is a language understandable both to human readers and computers - it is vital for the creation, and distribution, of RSS feeds.
An RSS feed, or Rich Site Summary, is a simplified way of delivering updates concerning webpages that are always changing. The BBC, Twitter and Facebook are prime examples.
By standardising the format in which data is delivered, it also becomes possible to publish data once that is then readable by a huge number of devices and websites - it rids us of the necessity to republish for each end user. Your phone, desktop and tablet can almost definitely access these feeds and display them in a uniform fashion without any extra tailoring on the part of the publisher. By bringing all feeds into one place (ie a single app, such as flipboard) it is possible to aggregate a huge number of news feeds into one location, this saves the consumer having to open facebook,
then BBC News,
then, well - you get the point.
On a theoretical level the presences of RSS means that we do not need to visit webpages as often, or indeed at all, via our browsers, as any updates or new material will be brought directly to us, thus saving time.
- when posting blogs and comments via blogger - you'll be asked whether to share the (exciting) news that you've posted via RSS - this will automatically alert any subscribers to your new output.