A couple uses for a Tarokka deck

1. Use it to play a horror vatiant of Zak's STACK game, which is "fast, light, cheap instant RPG for long train trips".

2. Use it in Ravenloft to make things more dramatic. Make a pause and put the "Beast" card on the table before announcing that the moonlight triggers the lycantropic transformation in the character who was recently bitten by a wolf.
Or give them to players as rewards, let them use them to boost their actions. A "Paladin" card could help with some noble deed, like disarming a cornered enemy or persuading a jury to free the wrongly accused, a "Rogue" card could help with sneaky stuff.