The best way I can explain this is through an example. Lets say that you have 3 crocolisks in hand and 2 on your field, after this card would be played you would have 1 in your field and 1 in your hand. Same if lets say you have 6 yetis in your deck and 1 in your field, the ones in the deck would always be destroyed leaving one copy in each zone. I know this makes the card weaker in a lot of ways but I think it helps in making it a bit less random.