CSS is designed to be very fast, and because of that design choice it's less expressive. XPath is not going to beat CSS in speed, but it allows you to move through the document in any direction (up and down in the DOM tree of elements, forward/back among siblings in the DOM tree, and forward and backward in document appearance order).

We use XPath at work from CSS with custom plugins, and use XPath in JavaScript for targeting elements that otherwise wouldn't be straightforward to select with CSS.

Another cool thing XPath does is have awareness of the text content of elements! //li[contains(.,"example")] would target all <li> elements with text content containing "example".