Some writers eschew discussing anything but game contracts and slams. I do not agree with that approach. Here is a part-score deal where, even though there was not much at stake, the end position is so striking that I am happy to share it with you.
South declared two hearts after a Flannery opening, and West chose to lead the spade seven rather than a top club. East ducked dummy’s king, and declarer then immediately played three rounds of diamonds to score a ruff in hand before giving up a club. West won that and continued spades, East taking the jack and ace before leading a fourth round of spades, on which declarer played the trump eight.
Dummy retained only its trumps after following to the fourth spade, so the defense needed to score three trump tricks to defeat the contract. If West did not overruff South’s eight, declarer could simply lead the heart king and then ruff the next minor-suit lead low before leading the heart jack to flush out East’s queen — no good. Instead, West correctly overruffed with the heart ace and then had to be careful to return a club.
South ruffed the club in dummy and had no choice but to unblock the heart king from hand at trick 10, after which he had nothing but clubs to play at the finish. Thus, East’s heart nine came into the picture. If dummy ruffed low, East would overruff, but East would instead discard if dummy ruffed high. Had West played anything else after taking the heart ace, declarer would have had a safe club ruff entry to dummy after unblocking the heart king.