Regrowth can be great - it adds regeneration to your carrion (and other undead). It's mostly useful, imo, when it goes on the larger carrion critters, and also on the carrion lords themselves (and Ambicephalos, the carrion dragon pretender, and undead commanders).
It only effects one square, but is in some ways more useful, or at least reliable, than the battlefield-wide Version, which is so easily resisted (there's an easy MR check) by the manikins and such that it leaves most of the carrion unaffected. It's actually something that makes MR-piercing items useful for friendly spells with CW.
Edit: And don't forget Mend the Dead - healing 50+ points of damage per cast really helps keep the carrion elephants alive. Also, having several carrion lords on the field to cast this on an undead warrior ( bane lord, an equipped bane lord, ambicephalos, or the carrion dragon ) can really help the combatant to stay up and fighting.