I think people mostly fear "normal resolution" in the Cab and Reverb blocks. Normal is a very high standard on FAS gear. For many, it's a mind game; the fact that they aren't using the highest means it must sound bad. It doesn't. Honestly, if FAS removed the higher quality settings, I don't think many could tell and there would be less CPU complaints.
FAS gear gives us many more options than other products, but with great power comes great responsibility. They give us options that purposely use more CPU than it needs to. If we choose those options, then we have chosen to have less CPU available for other things.