I use Manual Mode when I am towing a caravan. It allows me to save fuel by engaging a higher gear than the auto box would use. Plenty of engine torque but I am not interested in acceleration.
It is not quite manual gearbox as you normally don't have to change down a gear as you appoach a junction etc. (The box still changes down to protect itself from the driver). The driver only has to change up.
As said above - deliberately changing down is also useful when going downhill with a caravan - simple engine braking.