A low card, especially a 5 or less, useful for making a low hand.
Getting a card that will likely let you split the pot.
Winning the entire pot, either with the best high hand where there is no low, or by having both the best high and low hands.
A useless card that cannot form part of a low hand. E.g. a 9 or higher card in an 8-or-better game.
Two consecutive cards that improve a player's hand.