The whole "take less damage" reasoning is really kind of mute. For the most part, any physical raid damage that is a real danger is made to ignore armor.
My reasoning for wanting a shield is the same as Verdell. It feels odd not to have one.
Yea, there is only one mechanic that I know of in all of Soo that a holy paladin could be hit by that affects armor, which is engulfed explosion on Iron Jugg - which a hpal cant really soak anyway without going immune so the armor is meaningless. In MoP nearly every raid mechanic that is physical damage is not mitigated by armor, people used to value shields because in previous expacs armor did mitigate damage but it doesn't anymore.