When you have exactly 20 teams and cannot do pools → double elim with byes. Worst use: Casual tournaments where spectators need simple brackets. Final interesting fact: In a 20-team double elim, the team that loses in Winners Round 1 must win 6 consecutive matches in losers bracket to reach grand finals. In a 16-team bracket, that number is 5. The extra match makes the comeback statistically 40% harder.