It certainly takes far, far fewer shots- for some characters just a single clip of ammo and you've taken out that Vase Weed or Coffin Zombie as opposed to running through several clips to smash the armor, then the head protection and then finally vanquish it.
It's the same deal with the Shield carrying varieties if you fire over or under the carried shield.
Another awesome tactic during Graveyard Ops specifically is to use the Foot Soldiers Zombie Stink Cloud as cover during Boss Waves or Super Boss Waves because it effectively blinds the AI and they don't shoot you if they don't see you so just throwing it down between you and a Torchwood Boss gives you a short break from being shot at and set on fire. It can make finishing Crazy difficulty much easier and is useful during Zombie Boss Hunts.
