Guessing b is for braking mode for use downhill so you don’t have to use the brakes as much it uses engine braking. Used to drive a truck many years ago and it had a stalk on the wheel and you just pushed it forward to brake rather than use your foot and only when you come almost come to a stop do you need put your foot on the brake pedal. Like on ev’s they have brake re-gen which slows you down..
In the golf it used to have coasting mode in eco..which was fun, but one would have to use the manual mode to get revs up to use engine braking which you might not want on all the time in certain driving conditions