Nice question. Yes, it seems like if you need cliffs or other vertical structures, it may need to use meshes to cover these areas, i.e. I quite like images in this thread which illustrates how mesh is fitted with terrain:
Holes alone won’t do much, it’s all about the way how you craft that mesh and how you make it to connect nicely with terrain in places where you need vertical structures.
I am still wondering if there might be nice ways of doing this fully procedurally