Lets you essentially lower the heightmap resolution used for rendering.
This can be used on low end cards to never display the highest lod terrain. A value of 0 means always showing highest detail. A value of 1 means the triangle count will be reduced to 1/4th. The heightmap resolution will be halved for width and height.
using UnityEngine;
public class Example : MonoBehaviour { void Start() { Terrain.activeTerrain.heightmapMaximumLOD = 1; } }