Developing tricks in the trump suit (not no trumps) is the fourth method of finding extra winners. Look at any shortages (doubletons, singletons or voids), in the dummy hand (called dummy points), and sometimes delay drawing trumps until you’ve trumped losers in that short suit. You won't develop extra tricks if you trump shortages in the long trump hand, but you will if it's in the shorter hand. .
As a defender, if you notice declarer is not drawing trumps early, this is usually a sign for your side to play trumps, because declarer is planning to trump a short suit in dummy, or make each trump separately by cross trumping.
As well, when you have seven cards (or more) in a side suit as well as your trump suit, the potential for making extra tricks increases. Trumping some cards in this suit will turn the long cards into winners eventually.