Question about JTE's "hardware fixes"

[Sky The Destroyer]

I was looking around in the SRB2 source code, and found a line that defines JTE's hardware fixes. I decided to see what would happen if I turned it off, and it brought back shadows. What does JTE's hardware fixes do, exactly? (Besides breaking shadows)

 

[Liliam]

If it's what I think it is, go look at the tall slime waterfall area in THZ1, it should be obvious.