if we all had perfect spacial thinking and effective communication skills, we wouldn’t need a battle grid in combat. The DM could describe the dimensions and shape of a room in the dungeon, as well as relative positions of inhabitants and features. We could just describe how far we’re going, all adjust our mental pictures appropriately, and voila: the entire time to set up a battle would be the time we need to talk about it. Unfortunately, we don’t all have that. Some of us are terrible at it (me) while others of us are really good at it.