Helical just puts more resistance on the tail end, much like a tail on a kite. It also puts a spin on the arrow from the tail end. It's just another measure of correcting arrow flight. If your not having issues I wouldn't refletch.
I am however a fan of building in all the forgiveness I can, so I do use helical fletching on my arrows. How much is really determined by the OD of your shafts. It's hard to fit hard helical fletching on skinny shafts. My fav is a 4 fletch pattern with feathers. Lighter than vanes, maximum correction.