To summarize the past conversations.
-Paying for Carapace Armor for the entire army isn't point efficient.
Ok, now heres where we have touched.
-Paying for Carapace Armor for certain types of units are benefitial but may or may not earn their points back in game.
Now in which cases would you say buying carapace armor for an unit which WOULD make their points back. Maybe thinking about Hardened Vets, Rough Riders (previously mentioned), Special Weapon Squads, Heavy Platoons, etc?
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I personally don't believe in using carapace armor for the entire army just as it is mentioned, it isn't point effective. I don't beleive in carapace armor for normal guardsmen because I want to keep them at a low cost and dispensible (you can tell i'm not that nice to my guardsmen).
It makes sense to me, why pay 2 extra points per model to increase it's survivability when it's weapon and combat stats are mediocre! I say save the armor of veterans or assualty command squads.
Anyways, utilizing cover saves can save you points off buying carapace armor.