its when your in overdrive..it is a option that lets you overide ........and yes...its pointless and useless..been there
I pressed it while driving and I tell no difference. Wondering why it's even on there.
It will let you start out in a different gear (such as 2nd or 3rd) in bad weather conditions. It allows you to control the shifting as opposed to it being done automatically.
If you push the button, you have to move the lever to a lower gear for it to work.