Hi,
is there a reason you use planes to block the shadow? It seems like an awfully weird method as I was searching and found that you can instead just make the material double sided? WIth very irregular shaped cliffs it’s almost impossible to block them in a believable way like that. I have no idea if therfe are drawbacks on what I’m doing though 
Someone correct me if I am wrong, but I believe that making the material double sided essentially “doubles” the number of polygons in the scene.
For a small scene like the teacher is showing us it’s really not that big of a deal to double the number of polygons, but I’d imagine scaling it up to a more open world type map like Skyrim or GTA would hurt performance significantly.
Maybe there is a way to have the polygons block light both ways in some of unreal engines collision mechanics without double siding them? Which could already be what you are asking about, I still have much to learn about back face culling
Double-Sided materials don’t actually double the poly count, they take the normals of the existing polygons and flip them when shading.
This does effect performance if done at a large scale, but if you use it sparingly then you’ll be fine.