It's useful to have a common language for diagrams (actors, storage, etc)
It's not useful for more than very abstract concepts though. If you're UMLing your entire Java app before you add another class/method/function, you're doing it wrong.
Yeah we don't go that overkill, we really just diagram surface area (how does the backend communicate with the frontend and through which apis and when, and when should the front end expect a socket message, etc)
As a method of communication between projects, it works wonderfully
It's not useful for more than very abstract concepts though. If you're UMLing your entire Java app before you add another class/method/function, you're doing it wrong.