XML is frequently used in the publishing industry, business documentation and databases as it is easy to understand. Both coding and content are readable for the user. There is a logic to the coding that is fairly easy to grasp, because it is mainly user defined. For example, even when the data only needs to be understood by the computer, we can still understand what it is:
If we read the tags we can work out quite easily that this is "Jane Q Public's" contact information, and that she is the first in the database. XML is great for this type of information, as you only need a name, number, or email address to find out the rest of the persons information because all of the information is grouped.
Essentially XML is a great method of organising data. It's easy to understand, things within the code are much easier to find, and because everythings tagged and grouped it's very difficult for something to go missing when you want to transfer the file. It's not hard to see why it's becoming more and more popular.