If you have been making cliffs by triangulating every single brush or by using tetradehons everywhere, please stop and pay attention. By using the methods of triangulating or tetradehons, you are needlessly using resources and this is no good if you have a large amount of terrain. Instead, build your terrain in a way that looks natural while keeping as many faces flat. It is fine to split a face from time to time to mix things up, but remember to use the clipping tool more than you use the vertex tool. In the example here, only a few faces are split and most brushes are still quads. Remember that next time you build terrain.