The situation I've seen happen several times is that the AI will wait until after it's attacked to play spirits, which cause Tallowisp to tutor for Auras. There's two separate problems this causes:

a) The auras could help it attack, obviously, and it only gets them after combat. The AI didn't have anything to play or activate during combat, either, so it was pure waste.
b) It can sometimes not play them if it gets them after combat. I've just seen the AI play two spirits for total 3 mana, tutor two auras from Tallowisp after combat and pass the turn even though they were the only cards in it's hand and it could play wither of them.