Light loads — a picture, a shelf of books — can go into the board itself, because the board has usable pull-out strength. On a 10 or 12 mm non-combustible board that figure is around 50 N/mm of edge, which is enough for a domestic shelf but not for anything that a person leans on.
Heavy loads need to reach the frame. The first option is to set out the studs so the fixing lands on one: a wall-hung basin or a radiator is normally specified with a fixing drawing anyway. The second option, where the layout does not allow it, is a reinforcement module fixed between two studs, which spreads the load over a plate rather than a point.
The third option — and the one that gets people into trouble — is a cavity fixing in the board. These are rated for a pull-out load in a laboratory sample of the board, not in a wall that has been drilled, cut for a back box, and had a service hole punched next to it. The board around a fixing is only as strong as the nearest cut edge.
The design rule is to decide at drawing stage which walls carry heavy loads and to reinforce those walls as a system: studs at closer centres, a module at each fixing zone, and a marked-up elevation showing where the fixing points are. Retrofitting a reinforcement into a finished wall is possible with the clip-in system, which is one more reason the reversible detail is worth its cost.