Do you NEED them prolly not. They can be very useful in correcting cars that cannot be aligned to spec due to a variety of ailments. They can be used to gain more positive caster while retaining neg camber than possible with normal bushing. They can be used to compensate for cars that have frame "sag" where the uca mounts has pushed inboard.
Be aware that those bushings are more often than not frozen to the adjusting cam bolts and require cutting out. So make plans to acquire a new set of cam bolts unless you know yours has been apart and had some kind of anti-sieze material install.
Since we know offset bushings help acheive alignment specs for best radial tires and we know the poly upper arm bushing can squeak, why wouldn't we go for the Moog offset rubber bushings.