They are widespread among surfers - although opinions differ. Some couldn't do without surfing, others find it annoying. The function of the grip deck/traction pad/foot pad is essentially the same as that of the surf wax. Due to the 3-dimensional structure, they offer the foot additional resistance.
Position of the grip deck
The grip deck is glued to the board at the point where the greatest friction is desired. The best known is of course the tailpad, which is glued to the base of the rear foot. As a rule of thumb, place your back foot level with the side fins. Of course, this can vary and it is worth finding out the location beforehand. But there are also surfers who stick the whole board together. Front pads are mostly in demand where you don't have to paddle lying down (e.g. wakesurf, riversurf, bungeesurf).
Advantages of a grip deck
The decisive advantage of grip decks is, of course, that they work regardless of temperature, work forever and offer optimal support. The Gripdeck doesn't stay behind in your clothes. Often it is also helpful to immediately jump into the right position. When duck diving, the board can be controlled better and guided better under the wave. Last but not least, the color of the board can be customized with the Gripdeck.
Disadvantages of a grip deck
Short term more expensive than wax and shorter wave check during board waxing. With completely new pads, there is sometimes irritation in the knee area because the pads rub when paddling. The trick there is that you only very briefly break the "sharp" edges of the pad with sandpaper.