3D models, as you saw in Chapter 9, Generating a 3D Planet, can be extraordinarily complicated. It is natural we created programs that allow designers to sculpt in a digital 3D space as opposed to trying to create an algorithm that would generate these 3D models. A simple sphere can take thousands of lines of code to create alone.
Allowing a person to sculpt and see the creation of the model as it is being created allows for an unparalleled level of detail. It would simply take too long to try and procedurally generate every 3D model in a game. So, we generally stick to procedurally manipulating models.
The trade-off then is to make small pieces of a model that can be widely used and then having those procedurally constructed into a whole model at runtime. The effect is that we create a game world that is unique to that playthrough. It could be possible that the game world morphs every time the player starts a new game or just that this game world is unique to another player's game...