The game designer consciously provides a best strategy (or strategies) for beating a level or encounter in a level.
With, EmergentStrategies, some of the game design community is trying to move away from 'scripted' scenarios where the game designer has in mind how to beat the level. But, as described in the 'Deus Ex' post-mortem (http://www.gamasutra.com/features/20001206/spector_01.htm) (free registration required), when this effort fails, you may have to fall back on tried-and-true. Optimal Paths in level design is also discussed in 'Game Design: Theory and Practice' by Richard Rouse III.
Many games only have optimal paths; there is only one way to get through a given encounter. (Zelda, for example.) Deus Ex is one of the few games that provide multiple solutions to given problems. This pattern can apply to RTS scenarios as well: you can brute force through a typical RTS scenario, but many RTS scenarios provide nonobvious ways to beat the computer more easily.
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