How low would you go......regarding tire pressure that is?

remember when you air down tires on a dually you don't want to go so low that the rear tires kiss each other. Never having aired mine done for traveling on sand or snow I don't know where that would be. I have aired tires down on srw trucks but never when I had a max load on them.And I do it with my jeep but even then I air back up before traveling at road speeds.