That's not previsualization. Nothing "pre" about it. That's what he's seeing and getting at the time in the viewfinder. He's seeing it in real-time. Every photo you take does that. You change the lens, you see a different picture. You move the camera and change the angle, you see a different picture. We're making it seem like some sort of black magic. Maybe I;m missing something.
It seems to me that you are spending too much time looking through the viewfinder

.
The decisions about point of view, angle of view, reflections, light angle, distance from camera to subject, desired feel and mood and a myriad of other things are generally made by most of us without having a camera up to our eye. That is particularly the case for those using view cameras.
We use the finder to tweak the results - knowing all the time that the view through the finder will be a mere approximation of how a print might appear, because the printing process is still to be invoked.
The view through the finder is an approximation even for those of us who shoot colour transparency film, although the results in the transparency will be a bit closer to that finder image. We still need to visualize how the transparency will look, while we look at the very different view in the finder.
An example (from a digital exposure in this case, because I have a before and after at hand)
Before (as seen in the finder):
After (as visualized at time of exposure):
The differences are subtle in this case, but if I didn't visualize them first, I probably wouldn't have taken the photo.