> I would honestly ask your help to enlighten me on the necessity of XSLT. I'm totally willing to be wrong here. Can someone explain me how it is used?

It's pretty hard to beat when you need to transform some specific XML format into something else. Which isn't needed as often these days since XML is less popular than it used to be, but if you're stuck with XML, then XSLT is still a good choice.

For example, I personally use it for parsing video game save files and for displaying my Atom feed in a prettier format [0]. It's certainly possible to replace both of these with pure JavaScript, but XSLT is a really elegant solution here.

[0]: https://news.ycombinator.com/item?id=45873669