Adjusting play based on deck penetration involves analyzing how deeply the cards have been dealt from the shoe or discard tray in card games like blackjack. When there is high deck penetration, meaning a significant portion of the deck has been dealt, players can gain a better understanding of the remaining cards, which can inform their betting and playing strategies. For instance, if a player knows that many high-value cards are still in the deck, they might increase their bet size or choose to play more aggressively.