I see the value of that function mostly in public spaces. When you sit on the train, in a plane, waiting at the airport, etc it's currently difficult (though not impossible) to bring a good screen setup, and the risk of shoulder-surfing limits the kinds of data you can work on. A VR headset theoretically solves both issues.
Of course Apple are hardly the first to promise this, and ever other implementation I've tried so far suffered from being incredibly inconvenient due to the low resolution of VR headsets. The Apple Vision Pro at least has 4k for each eye, which should allow you to simulate 1080p screens at a comfortable distance. That might be enough to make it viable if the controls work out good enough. Still not enough to beat physical monitors when you have the space for them.