Once you have lowered the lever fully the engine won't be supplying much power, even with the governor maintaining 100% rpm: just check the manifold pressure.
But you are right, for a proper auto, the throttle should be rolled off to split the needles. It's fairly normal these days to leave the governor on - but with the throttle closed so the engine rpm drops below 80% and the governor stops 'governing'.
In particular, you need to get a feel for controlling rotor rpm during the descent - raising the lever a little if rpm starts to increase, and flaring out to prevent rpm dropping below 100%.
Was taught this very well a few years ago by a good instructor who showed me how to 'feel' my weight through the seat as we descended. Loading the disc slightly would bring the rpm up, and unloading the disc cause the rpm to drop. Turns also load the disc and raise the rrpm, requiring a little input from the lever.
Leaving the throttle open will completely mess this up as the governor will keep intervening. And how would you do range autos (80kts, 90% rpm)?
If you ever get to practice auto all the way to the ground you'll definitely need the throttle in the detent before you raise the lever !
Finally, there is the 'fear factor'. I reckon it's quite important to get used to flying with the needles split to build your confidence and to reassure yourself that you are not going to die if the engine quits.
Plenty of carb heat for _at least_ 30 seconds before lowering the lever and there is no reason to be afraid of splitting the needles.
Discuss all this with your instructor and find out the reasons he/she prefers to do autos this way.
[ 01 March 2002: Message edited by: Grainger ]</p>