Welp, this "practice" is pretty common for 4x4 guys... it's called "Airing-Down".
Anyway, I frequently do it.. as a lot of the trails I ride have paved path to get to them. So, I'll have 50-60 PSI in my tires for the paved part, and then lower them to 25-30 for the offroad. When I get done with my ride.. I'll C02 them back up a bit, or if I forget my inflator.. I'll just put up with the slow rolling resistance till I get back.
-Matt