It's pretty much the exact same thing - let's you specify a file to access with a string (pathname) such as "/foo/bar/cat" rather than having to go step by step first open/reading directory "foo", then open/reading directory "bar", then finally accessing file "cat".
With XPath and JSONPath you're just dealing with DOM nodes and children rather than directories and children.
Except that XPath and JSONPath are overpowered. I'd welcome a simple standard path syntax for JSON, for instance, I'd want to use for reporting schema errors in JSON document ($.users[10].name must be a string). I can use JSONPath, sure, but even this subset is annoying to parse - compared to a filepath which you can parse with `path.split('/')`.
Agreed - for a lot of use cases all you need is a pathname-like way to refer to elements in the DOM, not a search/filtering mechanism.