Well, you can do that, anyway.
There are some benefits to being able to assess the scene from different orientations, I guess - which you get used to using a large format camera (after a while, you stop being surprised when you look at the ground glass). But the vidom
doesn't flip the image over, just laterally (so, if you hold the camera sideways, the view is upside-down, but not if you hold the camera in landscape orientation). Using it requires moving the camera in an unintuitive way when framing a scene.
As for Cartier-Bresson, there seem to be a lot more photos of him
not using a viewfinder than of using one.
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I guess he gave up on it after a while.