At any scale, you use what is convenient to your goals. Think about maps. If you want to hike a mountain in Colorado, you might go with a topological map where 1 centimeter equals 2 meters. If you'd like to hike the Appalachian Trail, you might want a map where 1 centimeter equals 50 meters. If you want to drive around New York, you might want a good street map where 1 centimeter equals 200 meters. If you are teaching the history of World War II, and you are focused on the Normandy invasion, you might want a map where 1 centimeter equals 500 meters. If you are teaching world history and you want 1 map of the world, you might want a map where 1 centimeter equals 100 kilometers.

What details you leave off the map, at each scale, is always a hotly contested issue. You could create a world map with the same level of detail as your topological map of the Colorado mountain: 1 centimeter equals 2 meters. However, the map would be too huge to work with, and it would contain too much detail. You remove detail to keep the map convenient to work with, but it must always be convenient to the task that you are working on. You will get yourself into trouble if you work with too large or too small a scale. I remember when I was young, I was often frustrated with the high-level maps we used in history classes, as the scale was often too high for me to understand what was actually going on. I recall seeing the map of the 30 Year War, a bunch of big red and yellow and blue arrows invading different parts of Europe, and it really told me nothing at all about what happened during the war.