Anyone working with XML content can benefit from learning XPath. XPath is the way that elements are identified and located inside an XML Document. Want to find the first title in your document? Or the fifth? Or the 2nd one that also has those 3 special notes following it?
Stylesheets are easier if you understand how to write an XPath expression. It just takes practice to learn how to structure the question that you use an XPath expression to answer.