I am going to split hairs here but for the record,hunting arrows and even to a small degree,3-d arrows can be a little overspined and most will not be able to tell the difference,so with that out of the way.


For hunting the only reason is tuning.A properly spined arrow will absorb the energy from the bow and not shed the energy.

The arrow is a shock absorber as well as a tuning fork.The spine has to be close to absorb all the energy and not kick .An arrow that even wants to kick doesn't tune as well as one that absorbs and rockets forward.This will be a big advantage when trying to get field tips and broadheads to hit the same spot.

The tuning fork scenario really comes into play downrange at extreme distances.A properly spined arrow will vibrate all the way to the target just like a tuning fork,when this is lost,so is stability.That is why you see fita arrows and such with so many different spines.Another reason is for finger shooters for whom spine is a huge factor.