Lets you go really really fast. Can combo with halfpipes and their funky physics to let you jump really high too.
To perform the boost, hit wall ride at the corner/edge of two signs that touch each other ***perfectly***. I do not know if it's frame/pixel perfect, but I was able to get like 25% reliability.
In a future video I will show how the boost can also be activated without needing two signs to be "touching" like in this video.