Perfect play is only meaningful only in scenarios with perfect information and no chance, since otherwise it is impossible to determine with certainty what the outcome of a given strategy will be.
In practice, the optimal strategy might be impossible to determine even when there is perfect information, since there might be too many possibilities for a human or even a computer to exhaustively analyze. This is the case in games such as chess. In such cases the notion of perfect play mainly serves as a yardstick to measure practical strategies or algorithms.
See also: Solved board games.