Most of the holdout devices used today have been invented in the 19th century.
The main purpose of any holdout device is to temporarily hold a card out of the game, so that the cheat may retrieve it at some later convenient time. Only one card out of play can tremendeously increase the odds of wining. Not only that the cheat knows the identity of this card (an advantage that no other player has) and knows that it couldn't possibly be dealt to any other player, but this card also serves as if an extra card was dealt to the cheat on every round. In effecft, this is as if the cheat was dealt a bonus card, so that he may decide which combination of cards he likes best and finally discard the unwanted one, only to possibly use it on the next round (or at least switch it for a better one).
Some of the most popular holdouts are: