As I've rediscovered time and again while hunting and hiking; if you haven't been to a place in a couple of years you may recognize landmarks but not remember exactly how they fit into your mental map of the area. This kind of problem would have been deadly in places like Greenland, so any kind of mnemonic could be a life saver.

Also, when you are hungry, thirsty and tired, self doubt can be debilitating; a map can give a little extra assurance that you are heading towards fresh water.