When it is helpful to activate the differential lock?

You answered correctly. Activating the differential lock is useful when you have become bogged down and individual drive wheels are spinning, or when you are slowly driving straight ahead on slippery road surfaces. In these situations, the differential lock ensures that both drive wheels turn at the same speed, which improves traction and helps you get moving again. However, it should not be used when maneuvering on dry road surfaces, as this can cause damage to the drivetrain due to the lack of wheel slip. Always remember: use the differential lock only when you need extra traction on slippery or loose surfaces.