Off the pavement I'm in 4x4 for traction and control. Sometime I'll air down to improve the ride but not always.
The exception is on shale, fractured or blasted rock. On these roads I never air (70psi) down the 3,400lb tires on the truck. I air up the 1700lb tires to (45psi) on our Subaru past max (40psi) recommend to expose less sidewall. With the Subaru I stay away from the sides of the road where the larger stones are.
I'm running tandem Viair (old model) 300C. Bought the dual pack on sale at 40% off. This gave me redundancy for less than the cost of the better built compressors.