This myth is based on the reasonable idea that eggs crack, when being hard- or soft-boiled, because the air in the shell expands from the heat. The pinhole is supposed to release this pressure. Reasonable, yes, but tests show that a pinhole really does not reduce cracking. Rather, cracks occur either because the egg already has an invisible crack in the shell, which expands during cooking, or because the egg is being knocked about in the pan by too-active boiling.
I do the pinhole routine and always notice air bubbles escaping. The egg inside winds up rounder without the flatness from the air bubble and I haven’t had an egg crack since using the technique. Could you elaborate on this? Thanks