Hi, from the docs:
The effect of this feature is heavily dependent on your game and hardware. If you do not have many textures, to the point where loading and using the full resolution mip maps does not use all of the memory pool Unreal Engine 4 has devoted to textures, you will not actually see a difference between high and low settings (outside of the change to the Anisotropy settings).
What you’re changing with that is your texture streaming pool size and anisotropy. If you’re below the max texture streaming pool size, you won’t see any difference from that. As for anisotropy take a large plane and look at it at a flat angle. Then you should see some differences.