Took me less than 5 minutes to think of the following:
1. Educational aspects such as being able to copy choreography by watching a virtual expert do it and still be able to see your own body mimicking the actions which she would not be able to do in VR (this could include juggling patterns, martial arts, any kind of complex motion)
2. Overlaying any number of AR layers on top of physical hardware, think of the idea that you could look at a complex circuit board and immediately get tooltip pop-ups over each integrated circuit and how they work
3. Building things in the real world located at absolute GPS coordinates and having them persist so that other people who are on the same shared AR "layer" see them. You could create buildings wondrous castles creatures and effectively create new layers of existence, and these layers could stack and be as deep as you ever wanted them to be
4. Being able to do virtual reality in much larger spaces so you could take your AR glasses and walk out onto a soccer field and then project a game such as you fighting a bunch of storm troopers while moving around physically in a huge field
Use case 1 seems to be a minor improvement over a video call on a decent monitor today, and this is assuming that the AR and other tech would advance hugely from where it is today, to actually be able to do realtime filming and rendering with high precision, perhaps even in 3D to get some real advantage.
Use case 2 seems more realistic, but will be limited by eye tracking precision, component idenficiaction precision, and occlusion issues. Input will also be an issue (choosing which tooltips to see).
Use case 3 seems worse than building things in VR, other than some fancy art installations. Why would I want a virtual object that I can't view from my own home? Also, interaction would be fantastically limited, making the whole thing disappointing.
Use case 4 suffers even worse from interaction issues, and it also seems like a downgrade from current technology, which allows me to play in huge virtual environments without even getting off my chair.