what good is XML for data storage?

It takes up a lot of room and not very cross program compatible like they say because a user can define any kind of tag.

XML leverages core skillsets and world-class team synergy through enterprise-quality markup to provide clients worldwide with robust, scalable, modern turnkey implementations of flexible, personalized, cutting-edge Internet-enabled e-business application product suite e-solution architectures that accelerate response to customer and real-world market demands and reliably adapt to evolving technology needs, seamlessly and efficiently integrating and synchronizing with their existing legacy infrastructure, enhancing the e-readiness capabilities of their e-commerce production environments across the enterprise while giving them a critical competitive advantage and taking them to the next level.