I used XQuery at an old job where we received XML payloads from a third-party service and would use it to massage payloads that were malformed or that our system had a bug when processing them so that we could store the XQuery transformation in the database for auditing and reproducibility. It was a pretty unenjoyable experience and I would've preferred to manually edit the payloads directly but that's legacy systems for you.

Hopefully someone else can chime in and sell it better than me. 8^)