This is based on a recent hand, loosely recalled.
A Q J 8
6 5 2
9 6 5 4
A K Q 8
K Q 7 5 3
West leads the 3 of spades against a no-trump game. If the distribution's good -- if West has the king -- it's possible for declarer to take 11 tricks: finesse the queen in dummy, then (crossing first to your hand) lead again to dummy's spades, repeating the finesse. You'll make three spade tricks, five diamond tricks, and three hearts.
BUT if East has the king, playing the queen on the first trick gives up that trick, followed by a likely four club tricks, and the contract is set. You can draw your own conclusion regarding the relative virtues of locking in the contract versus risking your neck chasing after overtricks.