I learned from older posts to exercise the 4LO and CDL back in 2011. I was experiencing grinding noises when the CDL tried to engage/disengage. It was later I learned it was doing that due to non-use. The vehicle still drove fine while trying to engage/disengage, the locker was just continuously trying to do it's thing.
Also, the 4LO quit working a few years back (also due to non-use). The dealership had to replace the actuator, normally $3500 but my extended warranty covered it completely. When it fails, the 4LO light will just sit there and blink indefinitely, but the vehicle is still drivable.
Ever since, I followed the once a month rule. But what I have been doing is after I park, I switch to Neutral and toggle the CDL and 4LO on and off a couple times. What I don't know is if just toggling them is adequate or if I have to drive a small distance with both to qualify as exercise.