I think you answered yourself: stereovision support. The mental context-switch needed to go from stereo to mono to stereo again is probably more expensive than

I think you answered yourself: stereovision support. The mental context-switch needed to go from stereo to mono to stereo again is probably more expensive than just going from stereo to nothing and back to stereo. I just tried it and closing one eye at a time made me sorta dizy. (disclaimer: not a trained eyetician ;-)