Duration draw is a collective term for abilities that increase the number of cards you have in hand at the start of your turn. Most of the effects that provide duration draw are Duration cards—hence the name—but there exist a number of landscapes and Reaction cards that can increase your hand size on a future turn as well. The primary use cases of duration draw effects depend on the amount of cards drawn. If an effect provides a net increase in handsize over all the turns it is active, it can fulfill a similar function to other draw cards. In any case, duration draw effects offer extra flexibility and reliability for your deck.
Duration draw is valuable in engine decks because it increases the probability that you will be able to line up key engine components to start your turn; the effect is therefore similar to guaranteeing a non-terminal draw card in a normal-sized hand. The power of duration-draw cards is mitigated by the fact that Duration cards remain in play for multiple turns, and can therefore be played less frequently than comparable non-Duration cards. Moreover, the benefit duration-draw cards provide is delayed; most of them provide little or no value on the turn you play them. One reason Wharf and Gear are considered very powerful cards is because they can provide both terminal draw when you play them and duration draw the next turn.
Most cheaper duration-draw cards, such as Haven, increase the size of your next hand by setting aside cards from your current hand to add to your hand later—thus increasing your handsize at the beginning of your next turn comes at the expense of being able to use those cards on the current turn. More expensive duration draw will typically just give you +Cards from your deck on your next turn, or occasionally cards set aside from somewhere other than your hand.
Duration-draw cards often provide defense against handsize attacks, since they can allow you to re-draw to a full-size hand after being hit by an Attack like Militia. However, this is not true of effects that increase your handsize at the end of your turn, such as Way of the Squirrel. because they increase your handsize before you're hit by the Attacks and are therefore almost completely negated by such attacks.
 List of sources of duration draw
 Cards that create more draw than they cost to set up
Varying amount of draw (in some cases these only transfer a card to a later turn or replace themselves): Monkey, Garrison, Crypt, Conjurer (generates surplus draw as soon at it is played on two or more consecutive turns), Tactician (in this case the card cost of setup varies), Siren
 End of turn draw
 Cards that replace themselves and increase future handsize
 Cards that can generate duration draw from normal draw and cantrips
The following cards can play Action cards at the start of your turn and thereby generate duration draw if they are used to play normal draw cards or cantrips: Prince, Ghost, Captain, Mastermind, Royal Galley, Contract, Delay, and Summon.
 Net handsize increase
 Variable amount of draw
 Handsize neutral
 Can make duration draw from normal draw or cantrips