Why use a quadmap for a shadow?

Why does the tutorial tell me to use a quadmap for a shadow when I can just copy my original drawing and put a shadow effect on it then simply use the transform tool? Why use a quadmap at all?

You could for sure use the Transform tool. The main difference between the Transform Tool and the Quadmap is that the Quadmap lets you adjust all 4 corners of the image, so that you can put the shadow in perspective on the ground.

The Transform, on the other hand, only lets you move, rotate, scale, and skew. If skewing does the trick for you, then you don’t have to use the Quadmap.