In pre-printed tabletop games, and even morein freeform adventures, we know our location from the start. Your pre-published map shows all three levels of the castle, along with a a list of shops and other points of interest in the town. The spaceship blueprint has a list that covers crew quarters, the engine room, gunner stations, etc. Or maybe your book doesn’t have maps or blueprints, and presents flavor text and broad descriptions of the the people and places it covers. Both maps and descriptions, even general ones, are helpful when you’re running a game, and can cut down prep time for a scene. For those of us who fly by the seat of our GM pants in sessions, though, these may sometimes become a hindrance when we haven’t had a chance to go over them in advance. When presenting players a location, knowing where things are placed, what's secret or hidden, what doors are sealed/locked, where all of the traps are and so on, are all things you should probably know ahead of time. But ...