The effect of parallax increases with magnification. For hunting, if you use scopes of up to about 9x, the effect is not usually going to be enough to matter, which is why your typical hunting scopes up to about 9x don't usually have parallax adjustment.
If you are target shooting, or shooting at very close range, or shooting a scope with magnification of 10x or more, that is where you might want to be able to adjust the objective to correct for parallax.
