It allows you to stay on the fence throughout those stages, this might be faster if not a lot safer than having to go through the saw stage and the rock stage.
Video: https://streamable.com/09a4e
I timed it over the 2:30 Any% WR and even with not optimal car movement it should be roughly half a second faster.
Wow! I never noticed. Today I actually found another trick to save around 6 seconds aswell, you'll see when I use it in a run. I can pull both of them off in a run
Actually, I'll just tell it now. Before you start a run, you get in the car and go straight backwards to the start of level 5 (after the 2 jumps) After that in a run, you can just take the car and pretty much just drive over the floor that kills you. It skips a big part of level 5.