Conrtolled risk is in every part of our training as pilots, but when an instructor gives up that control for only a few seconds things can very well go to crap. Think of it, the instructor shuts down the engine in flight, all procedures are carried out normaly, the student over flairs and now the aircraft is in a bounce, now nobody has any control over the plane and no matter how experienced a CFI is, he cannot 100% prevent this from happening and the risk started when he flipped the switches. At least if the throttle was pulled to idle, the CFI has not lost any control in the risk. Even if the plan was to restart the engine before landing, what if it didn't start and then you are in a position where you have to land it dead stick. Like i said, i can see the benefit of doing dead stick, but the CFI giving up total control is just too much of a risk, and IMHO too dangerous
Like Ballpoint246niner said in his earlier post, The CFI must be damn sure he can handle the situation or have alot to answer to. But when he gives up that control for 2 seconds things can go nasty.