I find tow mode useful when the engine is cold and you are taking off, towing or not. Yesterday, I got our Phoenix Cruiser out of the storage garage about three miles from our home. When the engine/transmission are cold it seems like it really struggles to make a hill outside the storage place. This clears up after a couple of miles of driving when normal operating temps are approached. The tow mode seems to help until then. Otherwise, I only use it like all the others have commented: downhill for braking. It is marvelous on some Colorado passes coming down the far side.
Paul