Prepares student for rapid change of flight from visual flight into IMC
I'd have thought that it would do quite the opposite. The transition from a visual take-off to instruments in very poor visibility is a difficult skill to learn and something that is very dangerous indeed if you get it wrong, particularly with a simultaneous engine failure, and I would have thought that practising and demonstrating that skill was more important than doing the whole takeoff run on instruments.
Incidentally, when I did my (CAA) IR training in the early 80's I was expected to do a landing entirely on instruments, not for the test but during training. The particular instructor, Dai Heather Hayes, wanted us to realise that if push came to shove it was more practical to land in zero vis than to eventually plough a furrow somewhere under the hold when the fuel ran out.
W