I believe i was talking about speeding up renders by creating assets with less pollys. Which happens later on in the tutorial when we get onto trees.

There is no one part that deals with this more a collection of thoughts on scene optimization as we go along. A large scale environment is just going to take a while to render.

Apologies for the lack of table of contents it slipped my mind, i worked on this tutorial for a couple of months and got so familiar with it i simply forgot.