When a GameObject in the Scene is far away from the Camera, you can’t see very much detail, compared to when the GameObject is close to the Camera. And even though you can’t see the detail on a distant GameObject, Unity uses the same number of triangles to render it at both distances.
To optimize rendering, you can use the Level Of Detail (LOD) technique. It allows you to reduce the number of triangles rendered for a GameObject as its distance from the Camera increases. You use several M