You can put way too much helical on fletching, actually to the point the fletching acts like a parachute instead of steerage. I've seen so much helical that when you look down the shaft, the back end of one feather overlaps the line with the front end of the feather next to it by quite a bit. Sure does stabilize an arrow quick and makes big 2-blade broadheads fly good with minimal tuning, but it really erodes downrange performance. Traditional shooters are the world's worst about that.

It also makes feathers noisier than need be in flight, hence that other popular myth. You really don't need very much helical to get the job done, as long as the bow is tuned and the arrow is the right spine.