You are not missing out on anything. I find it useless and the noise is enough to make your skin crawl.... It has a vary narrow use case in the real world.
It may require that you be in the D position... Can't remember..., played with it a few times and realized quickly it was not very useful.
Engine braking is what you usually want.. Shift it to first gear...
-4Lo
-In "Low or 1st Gear"
-Below 10mph
-Do not touch the brake pedal at all
It works fairly well when you need it (though to be honest, I rarely if ever have seen a need for it on most steep inclines), but it works REALLY SLOWLY... like so painfully slow I usually just go back to manual engine braking to get the job done.