That’s certainly critically important advice. However, it would seem that if an engine (at full throttle, which it would be in most partial engine failure modes) drops rpm to 1000 - 800, it ain’t really “partial” engine failure anymore. Also, one needs to be cautious about reacting too reflexively and feathering the wrong engine, thus the mantra “identify, verify, feather”. It only takes a few seconds. Still, if you see the rpm falling rapidly, get it feathered.