It's pretty common to leave some extra length past the upper string groove. It aids in using a bow stringer, and helps prevent having your fingers overshoot the limb if you use the push-pull method. A slender upper tip also looks more elegant (where you notice it). Keeping a stubbier length on the bottom helps make it "little" more resistant to damage and gives a "little" more clearance from the ground if you're shooting from a crouched position. The "functional" difference is subtle, but the variation is so easy to create, that there's no reason not to. I do the same with my limb tips.