Since no one else has chimed in, I'll do my best.
GND stands for Graduated Neutral Density. Mainly they are used in landscape photography to tame skys and prevent blown highlights. With the move to digital, they are to my mind redundant - better results can more easily be had by bracketing a shot and blending in photoshop either using masks or the HDR function.
I still use grads on a regular basis. In New Zealand last year I used a 2 stop soft for many shots taken during the day. It worked very well taming a too hot sky. The Lee 2 stop soft is very forgiving on placement.
I would hate to have had to blend that many shots.