On long and steep gradients, you must reduce the load on the brakes by shifting early to a lower gear. This allows you to take advantage of the engine braking effect and helps avoid overheating and excessive wear of the brakes.
When you take advantage of the engine braking effect, a drive wheel may not turn for some time, e.g. on a slippery road surface. This could cause damage to the drive train. This type of damage is not covered by the Mercedes-Benz warranty.