It creates havoc with keywords that require a certain number on hand to use the keyword effect with regularity. Unliving, Soldier, Beast, even to a lesser extent Illusion, Nature, Aqua, and Destruction can have plans torn to pieces by removing the commons from your hand. Don't even get me started on Titan being impossible with this as it is. It doesn't matter how useful the Holy cards may be. The loss of the common keyword cards, potentially many at once, can derail a strategy very effectively.