They think it gives them more spin. Usually you will see this in a blazer type of vane where the vane is 2", and not the usual 4". It has been shown that moving the vane forward does not help with generating more spin though. Some still believe that it helps, which is why you still see them fletched that way. I have done my own fletching several different styles, but truthfully, it does not make a difference in the impact point.