One major reason to use XML for a Web site or Web-enabled application is the capability to adapt content for viewing over mobile phones and other devices.
In some ways, providing content for mobile phones is just like providing it for a traditional browser; both use marked-up content. That's about where the similarity ends right now, however.
Web-enabled mobile phones do have a browser, but they have some extremely tight restrictions. Pages must be very small to fit both the screen and the tiny amount of available bandwidth (current phones can move as slowly as 9Kbps), and there are no large, color, graphics.
Even the language is different. At the time of this writing, HDML, or Handheld Device Markup Language, was being replaced ...