Comment by therealmarv

E.g. massive XML documents with complexity which you need to be transformed into other structured XML. Or if you need to parse complex XML. Some people hate XSLT, XPATH with a passion and would rather write much more complex lxml code. It has a steep learning curve but once you understand the fundamentals you can transform XML more easily and especially predictable and reliable than ever.

Another example: If you have very large XML you cannot fit even into memory you can still stream process them with XSLT.

It makes you the master of XML transformations and fetching information out of complex XML ;)