I think that method returns a URL made up of different parts:
(a) some standard & complicated parts, like FileManager.default.urls… and
(b) a file name (String), that you define elsewhere in a caretaker object
“This method simply finds the Documents directory and then appends the given file name”
I don’t think the URL changes once it has been initially created. It remains the same. The static method provides a way of referring to that same URL from other places in your code.
It just happens to be called createDocumentURL (which it technically does), but that doesn’t mean it creates a new URL each time. It creates the same URL each time. It just provides a way of referring to that same URL.