Cat. #1000 Straight Jig & Clamp: includes standard nock receiver and straight clamp; used for straight, and right or left offset fletching. (Recommended for target shooters)
Cat #1002 Right Helical Jig & Clamp: includes right nock receiver and right helical clamp. (Recommended for compound shooters and overdraws)
Cat #1004 Left Helical Jig & Clamp: includes left nock receiver and left helical clamp. (Recommended for compound shooters)
Cat #1006 Straight Jig & R.H. Clamp: includes standard nock receiver and right helical clamp. (Preferred by the traditional shooter)
Cat #1007 Straight Jig & L.H. Clamp: includes standard nock receiver and left helical clamp. (Preferred by the traditional shooter)
I'm guessing that the offset nock receiver rotates the nock a little to the right (or left) to keep the nock centerline aligned with the fletch midpoint to clear the type of rest used on some compound bows that require the fletch to pass through a slot.
If the majority of the fletch were to one side of the shaft centerline like on traditional arrows (rather than equally on the left and right of the centerline) it could not pass through the rest cleanly.
This could also affect the recurve target shooter depending on the type of rest used.
According to their guidelines above, if shooting off of a knuckle, shelf or weather rest, the straight nock reciever is what we should use.