What advantage of a map which shows only a small portion of earth's surface compared to a large scale map?

You can see more details depending on how "zoomed in" it is or how small the portion is. For example if you look on a map of the world you can see the landforms and bodies of water, but if you look at one of just the US you can see the different state borders as the state capitals, lastly if you look at one of just a single state you can see all the different streets and all the city's located in that state.

Where's the we need to see the it could be any country!

Granite is a hard stone and lasts for a long time in both modern and ancient buildings. as proof of its durability, granite is often used in gravestones and memorials, intended to last for many years.