Rule variations can have a significant impact on the optimal blackjack strategy. For example, if the casino allows double after split, it can be advantageous to split pairs when the dealer's upcard is low, as this increases your chances of getting a good hand and allows you to double down on a favorable count. On the other hand, if the casino does not allow double after split, it may be better to avoid splitting pairs unless you have a very good hand. Similarly, if the casino allows re-splitting aces, this can be beneficial if you have a good count, as it increases your chances of getting a blackjack.