I don't really use any. I always set up my bindings to the boot. Adjust overhang etc and adjust the highback to sit flush with the back of the boot on as large of a contact point as possible. If it hits up top of the highback but a gap at the bottom, adjust! etc... I have never used a lean adjustment for anything but flushing up my boot and making it all fit.
i used to find it helps for quicker and more responsive transition to heelside when i was starting out. but, i haven't used them in years. makes my legs tired faster standing in line. i should just rip them off to make my set-up lighter... in fact, that's what i'm gonna do tonight, rip them all off. with my teeth.
Most people that ride the park all day don't use any lean at all. It's a bit more comfortable if you're carving all day long on hard pack to go with a little bit. I usually go with what FLuiD said, but I make sure I have the top of the high back pulled off of the boot enough to fit a penny in there. This, for most boots and bindings is zero lean.