Here is the bottom line...
An open differential provides some traction as long as both tires are on the ground, and will provide zero traction when one tire is in the air. A locker will help most when it is used on the axle that spends the most time in the air. If you put a locker in the front and you pick up a rer tire, you have just created a fwd truck, and we that would create a ton of unneeded stress in the front end. Plus, the steeper the trail, the more weight that shifts to the back.
