If the instrument can be made with a tapered neck, it will give it greater strength when flexed sideays - the bending moment of a stress applied to the neck at the pegbox end will be greatest where it connects with the body.

I know somebody who imports Turkish instruments like sazes and tanburs. They are more prone to breakage in transit than anything else she handles - usually the neck snaps off the body. They have to be that shape because the left hand slides all the way up.   An ud is much tougher - as it's mostly played in first position the hand doesn't need to glide up as freely, and the neck can be both thicker and tapered.

Another one is walking sticks. They always taper towards the bottom. I assume it's partly for balance and partly so if they break it'll be near the tip and you'll still have enough stick in your hand to break your fall.