On wood arrows itis important to have the spine of the arrow lined up with the cock feather. Spine is measured across the grain of the shaft and that's the way it needs to bend. The spine position needs to come off thebow the same way. The bowstring needs to run perpendicular to the grain of the shaft. But aluminum arrows pretty much have a uniform spine around the axis of the arrow. I'm not much up on carbon arrows, so maybe someone else could chime in.

But remember that in the case above the cock feather is used as an alignment tool. It doesn't necessarily have anything to do with flight characteristics of the arrow.