I’m glad I’m not the only one who knows that trick. Works great when you have to thread a bolt by feel because you don’t have a good line of sight. Mostly, I do this installing oil filters where I’m lucky to just get my hand in place.
It's an old trick to prevent cross-threading. Gently rotating the socket counterclockwise while aligned vertically will let you feel when the plug's leading thread drops a tiny bit into alignment with the head's first thread gap. It's subtle, and requires a deft touch, but it does work.