By far the most 4x4 vehicles, falls into this class. The vehicle has a transfer case which can select normal 2WD, 4WD high range and 4WD Low range. If the vehicle is used on tar or any other hard surface, it can only be used in 2WD. The reason for that is that when going around corners and dips and bumps in the road, the wheels all travels slightly different distances.
That is the very reason why any axle of a vehicle, must have a differential. The differential will equalise the difference in distances travelled. If it was not there, the side shafts will simply have to twist up like koeksusters and will snap within a very short distance.
On a loose surface, the tyres can however slip and in that way, be relieved from the wind-up that will occur between the front axle and the rear axle when the 4WD is engaged. For this vehicle to come to a halt, one wheel on each axle must spin for it to stop. If there is grip for both wheels on the same axle but a wheel on the other axle slips, the vehicle should move.