The value of a Jokerless hand is doubled. For example, if a player declares mah jongg on a hand that can use jokers but it is jokerless, the value of the hand is doubled. If the player self-picks their winning tile, the value is doubled again.
The Higher the Value, the Harder the Hand (Article ID 42)
Jokerless hands under the Singles and Pairs section of the card have the highest values on the card.