You create your schema to be as explicit as you need it to be, validate your XML files using the schema, and your data should be just what you expect it to be. The heirarchical structure of an XML makes it easy to process. Each data instance has a know structure, each element has known characteristics. The structure can be used to access, update, or delete any data element. The perfect, predictable structure of an XML file allows you to download the data and its processing to the client.
Content Has Meaning Each data element has specific meaning and characteristics.
A date, for example, is identified as a date rather than just be a string within some text that looks like a date. Because XML understands Unicode, multi-language publishing is possible.