During the late afternoon when everyone is trying to ski out (or at other points during the day), Green Line is jammed with people.
It is narrow and also mainly a road, making it extremely busy and congested.
If you are looking to escape the madness, Grub Stake is a quick short cut that allows you to pick up some speed quick in the shaded trees and jump out the other end, linking up with Green Line for the final pitch to the village or parking lots.
It is mostly shaded so it can be rather icy, making it fast.
Grub Stake is usually quite empty in comparison to Green Line, and is a much quicker way to get down at the end of the day.