Zout, That is called phasing. As that shaft turns the u-joint speeds up and slows down through a 360 degree rotation. The joint on the other end have to be in phase so that the joints on opposite ends are speeding up and slowing down opposite of each other therefor cancelling out any vibration. That is why it is important to have the same u-joint angle at both ends of the shaft. I have seen many, many lifted trucks where the rear is rotated up too line up with the shaft at the same time the other end is a sharp angle. This will vibrate every time and joint life will be very short. The one exception to this rule is if you have a double carden joint at the transmission end. Then the two joints at the one end cancel out and the shaft will go straight at the rear.
Rick