If you use free wheel hubs,
you can stop the whole impulse-cord (impulse-shaft, differencial)
on vehicles with switchable all-wheel-impulse on the 2WD-working.

Profit:
fewer wear on the impulse-cord and the front-tires,
easier driving and fewer fuel-consumption
because smaller roll-resistance.

Further the manual free-wheel-hubs have the profit, that you know,
if they are switched or not.

Important:
please asways control both sides and switch opportune.