A few things not otherwise mentioned in other answers:
Grip depends on how much pressure you can exert via your fingers. Often times it is not advantageous to just get as much skin on there as you can. A good example is the occasional sloper - if you try to smear your whole hand on it it's much harder to not slip off versus just driving your tips down like a crimp.
On single/double finger pockets (aka mono doigt or bi doigt), you can often get really good pad pressure from just a finger or two versus trying to cram all 5 fingers in there. The pictured hold, in particular, often has a jug-like shape inside the hold, so you can really get two fingers deep in there and really hook in.
Hand anatomy matters as well... you can pull really hard on fingers that are crimped properly. If you scrunch up your fingers in a weird way that the hold doesn't accommodate, you can put your hands in weirder, more injury prone positions that don't afford as firm of a grip, or increase hand fatigue as you hold on and pull.