Unexpectedly, on the third day the long-overdue scouting squad returned and there was great joy and relief in the camp. The Commander questioned his men eagerly, "How did you survive, how did you find your way back?" The sergeant who had led the scouts replied, "We got lost in the snow. We'd given up hope and resigned ourselves to die. Then one of the men found a map in his pocket and we used it find our way back.
The Commander asked to see this wonderful map. It was not a map of the Alps but of the Pyrenees!"
Maps — even wrong ones — provide a visual aid for communication, challenging assumptions and learning as you go, rather than relying rigidly on a pre-determined course of action.
Understanding where you are, where you are heading and why there (and not somewhere else) is also critical for strategy1. This is why leaders over millennia have used maps to learn about the territory they're in, understand how it's changing (eg weather conditions), and which paths can lead to success.
While there is no such thing as a perfect map, any map that provides a reasonable model of the environment will enable you to make better decisions. But without a map you lack the situational awareness to make appropriate choices or adapt as you go, meaning you're simply guessing at what to do next.