Part time 4 wheel

It's the old way of doing things.  Normally you leave it in 2WD except for off-road or snow, conditions under which you don't usually want to tow a trailer.  There's an extra shifter for moving between 2WD and 4WD, and it won't instantly ruin your vehicle if you drive on hard dry pavement in 4WD, but it will tend to bind things up.  You can feel it when the wheels need to turn at different speeds but can't.  It's not good to leave it in 4WD unnecessarily though, you're right.  If the roads are at all slippery, you can use 4WD.  Maybe after the plows go through.  It's really not meant for rain though.Part time 4WD is the real thing and it can't be beat if you find yourself in a tight spot.  It just requires some thought and action on your part, whereas AWD uses its on board computer to figure out where to put the traction.  AWD is great for rain, pretty good on snow, and good for people who don't understand how to work an extra shifter.Also, generally, 4WD trucks have more ground clearance than AWD vehicles.  Sometimes a plus for serious boondockers.TT

Excellent picture!!

With my Suburban I use Auto mode in rain or when I could hit snow/ice patches.  If there is a steady coating on the road it will be in 4wd mode.  No need to rush to change it if you happen to hit a patch of pavement.