Left helical is a throwback to the pre-compound days when you shot arrows off the shelf of a recurve bow. It was felt that for a right handed shooter, left helical would give better shelf clearance. With todays compounds and cutout risers, left or right helical doesn't mean squat with respect to being right or left handed. HOWEVER, right helical is desirable for the single reason that when your arrow hits its target the spin of the arrow will tighten the broadhead or field point onto the shaft. Left helical can loosen a broadhead, causing blade loss. Broadheads with offset blades (like Rockets) are also offset to the right, so it is advantageous to have them spin in the same direction as the offset.