When plowing driveways, you are constantly doing a lot of jockeying around out in the street (bare blacktop) mostly. If you use 4HI, you can just pop in out of 4x4 and into 2HI on the fly and not bind up out in the street. While if you used 4LO, you have to stop and shift into 2HI. Whenever you see your tranny or engine struggling with deep snow, etc. Use 4LO. It will depend alot on what your rear gears are. If you run 3.42's you may want to use 4LO more than a guy with 4.11's.
I use them about 50 50, high for long runs, and small lots, where I don't plow for more than 15-20 min.
low range for long periods of for/back or when stacking snow. also when truck starts to labor under the weight of a deep windrow.
doing this keeps the heat out of the tranny because you are using gears as your torque multiplier instead of the torque converter. (previous experience, plus a tranny temp guage verify this statement. I do start in 2nd gear when in low range to avoid the hard jerk from the 1-2 shift. MY 1-2 is stifer than most for plowing snow and trailer towing.
Alot depends on the dif gear ratios, but the main is reasonis that I generally have the gas/auto combo with a 205 t-case, and that has a higher ratio 4 low than most other t cases. So we dont sacrifice back up speed. Also I have to agree with plow boy, in that I would rather use the gears and not not the tranny to move the big stuff.
I have an 84 with 3.54 rear gears, and those gears and high range really dont mix.