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This is useful. This came to me as I was working on a multi-level dungeon, and was wondering in the case of a room taller than ten feet and then another room under them that is taller than ten, so if it was pulling from a 10′ sphere around the caster that has nothing but stone (as enemy/allies are more than 10′ away). So in that case Barren would work and prevents a player from using that logic to just ravage for extra mana with out some type of negative action.