A partial list of game design consequences which arise from Vancian casting:
- Refers to Jack Vance’s The Dying Earth, never a bad thing.
- Introduces a pacing mechanic: oops, time to retreat I’m out of juice.
- Introduces suspense: did I pick the right spells?
- Allows new ways to measure skillful play based on how well you manage the gamble of spell selection.
- Rewards gathering information to make wise spell choices.
- Encourages repeated delves to improve casters’ efficiency.
- Creates a market for more reliable classes, and thus an adventuring party, to hedge against bad spell selection.
- Implies a very mundane (board-gamey?) aesthetic: magic is a commodity like torches, food, and arrows.
Naturally other magic systems might be better at these same goals, or achieve different goals entirely. But the existing system is pretty far-reaching in its effect on the game.