Some material types may include normal map textures. What does a normal map achieve?
It programmatically reduced the polycount of your meshes.
It is a level-of-detail system that progressively reduces a mesh’s polygons as a scene camera moves farther away from it
It displaces mesh geometry with extrusion and bevels to generate higher-poly versions.
It creates the appearance of surface detail on mesh - like bumps, dents, and scratches