If you're flying engines that have crankshaft counterweights, (PA31P/LYC-TIGO-541A) for example, the crank counterweights, bushings, and pins take a terrible mechanical beating that can set you up for a catastrophic mechanical failure by rapidly retarding/opening the throttle. Mixture cut-off only deprives the engine of fuel, while not rapidly changing the dynamic loads on the piston/rod/crank interface during the simulated failure (remember the engine is still breathing air during a mixture cut). Rapid throttle movements (even during normal flight ops) is alleged to promote detuning of these critical crank balancing components, leading to their failure. Back in my prior life, I did a lot of C&T with counterweighted engines and never had a failure or complaint from the engineers at overhaul time. Maybe somebody else with time in these machines could share some knowledge/experiences.--CY