Englishal,
Ever tried engine failure with mixture ICO in FL summer when density altitude can reach 2500'. If something goes wrong and you were able to feather the propeller in time, you wont be able to get any climb performance at all.
In our school we have a policy, no engine failure using either mixture or fuel control below 3000'. Below 3000' we use throttle only. FAA also recommends using throttle to simulate engine failure below three thousand feet.
Personally I don't think I would be able to explain the controlled crash landing to either FAA, NTSB or the lawyer if i were to go down with perfectly good engine not working because of something I did. I guess living in the land of law suits makes one more cautious.