Super rookie level building question

So I’m following an online tutorial, and they built a level by basically just kit-bashing a **** ton of rocks together. This seems wildly suboptimal to me, with a ridiculous number of polygons and textured surfaces hidden outside of sight all over the place.
Is this not an actual issue though, because of occlusion culling? Is this actually the optimal way to build a level? It would certainly save a hell of a lot of time.