My own opinion is that the risk outweighs the benefit of actually stopping the engine of a single at any point. The very small additional "experience" is really not worth the chance of something going wrong, and needing a stopped engine you can't get going again. If it must be done, it should be at altitude, and with a briefing. The affect is the same far form the ground, and close to it. I am required to stop and feather engines on twins during flight testing sometimes, it gives me the willys, and I orbit high over the airport.
There's no real need for instructor drama during training. Accidents happen then too, and it's nice to be able to explain to the insurance company that you were doing everything to mitigate the chance of an accident. Deliberately stopping an engine would not be that!