I've not noticed a degradation in performance in necking down from the larger cases and generally don't neck turn UNLESS it's necessary such as too thick a neck for the new round. If I had to turn a lots of meat off then I'd not bother.
The rounds I've done this on are 22BR from 6mm BR and 17 Hornet from 22 Hornet. The latter doesn't need turning to deliver sub-MOA (well, 0.3 - 0.4 MOA five shot groups) and the former had to be turned due to the required neck diameter.
I have turned the necks of my 22-250, 308 and 30-06 rounds just to see what happened and it wasn't really worth it but is simple enough of you bother to get the right gear. I use K&M kit and a bit of power assistance. With the 22BR I think I knocked up about 500 cases with much bother.