[Lordzy]

I find it quite useful while dealing with collision physics. Imagine you want to project the path of two systems' collision. You can project their collision and their displacement after collision visually using this include. If your debugging code is done in a proper way with this include, various tests can be done easily by simply changing the appropriate debug values. This helps a developer to view the results mostly in game rather than to test each and everything.

If you think of more relating to collision physics, there can be still more.

EDIT : Not only for debugging purposes, this include can be used to project lines that project till it collides. The author could've seen more purposes other than debugging only.