When the other side can't top it with a higher trump (bridge). When it wins the trick at least cost to you (saving a high non-trump card for later, bridge again). When you have to win and you pull out the ace in the hole. When the opposition doesn't know you have it and gets caught flat-footed from bad planning. When you have no other card to play.
When the other side can't top it with a higher trump (bridge). When it wins the trick at least cost to you (saving a high non-trump card for later, bridge again). When you have to win and you pull out the ace in the hole. When the opposition doesn't know you have it and gets caught flat-footed from bad planning. When you have no other card to play.