Several tactics that involve taking Foreign Aid: * You have two Dukes. For your first action you take Foreign Aid. Probably only the "real" other Duke will block you. * People keep stealing your coins with the Captain. You take Foreign Aid, a Duke blocks it. No Captain can steal your 0 coins. So, you've effectively passed. * You have the only Duke left and it is your turn: you take Foreign Aid. Player 2 takes Foreign Aid. Player 3 takes Foreign Aid. You block them. See the surprise on their face.
And last, at the end of the game when all Dukes are gone, the game goes faster with Foreign Aid.