Consider a simple business letter sent to a law office. Attorneys, among other business professionals, need to be able to track all correspondence. Some law offices have developed complex systems that store letters for retrieval using complex, coded directory structures. Others put letters into a database. Some perform full-text searches of the data by looking for names until they find the needed document.
But if attorneys start creating letters as XML documents, they could search using more specific criteria to find what they need more quickly. This system would reduce the amount of time required to service one client and free up time to pursue additional revenue.

As you can imagine, XML is not appropriate for every task. As in carpentry, users are encouraged to use the most appropriate tool to complete the job at hand. If this letter is never going to be searched for, referenced or read again, there is no point in making it an XML document. But if this document will be kept and viewed in the future, then thought should be given to structuring the information for maximum future usability.