Sometimes in Arkham Horror we tend to get obsessed with Min-Maxing. 21 or Bust is a card whose greatest strength is that it is just fun. It's enough of a gamble that the team feels tense when you are at 17 and want to pull another token, it's not game-ruining when you fail, and it's an incredible experience for the group when you actually manage to hit 21.
Outside of gambling, this card does have some utility through the reveal token text. If you're running Favor of the Moon for curse mitigation, this is a really good card to release a sealed curse on. The curse token itself has no downside, and you gain a resource as part of the effect.
Side Note: If anyone tries to give you crap for running this instead of Emergency Cache, remind them that there are dedicated fighters out there running .35 Winchester.