Here's how I understand it...
In a power divider with an inner axle differential how much torque each axle gets depends on how much traction to some extent.
With the power divider unlocked both are driven, but if one axle comes off the ground it'll spin, the other won't and you won't go anywhere.

The differential in the power divider acts same as the differential in the rear axle differentiating between two wheels, only it differentiates between the front and back axle.
With it locked both front and rear axles will turn together.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-