A Used Deck Can Carry Information
A deck is more than a set of cards once play begins: its order has changed, and its cards have passed through players’ hands. In blackjack, a card counter keeps a running estimate of whether the remaining cards contain more high cards or low cards than usual. That estimate can help a player adjust strategy. Starting with a fresh deck—or reshuffling—wipes away that accumulated count and gives the table a new starting point.
Replacing cards does not make counting impossible; the count can begin again. The point is to limit how long a player can build useful information from one shoe, the group of decks dealt together.
Why the Cards Are Destroyed
The other concern is hidden information on the cards themselves. A cheat might bend, scratch, or otherwise mark a card so its face can be recognized from the back. Even subtle damage could make a card valuable if it slipped back into play. Destroying retired decks makes that particular route harder: the cards cannot simply be gathered up and reused.
Casinos may shred or punch the cards after removing them from service. The physical damage is a practical security measure, not just a way to dispose of worn paper. The deck’s replacement resets the game’s information; its destruction helps keep that information from returning to the table.
