Running nail through a potato serves two purposes: It does allow steam to escape to minimize the chance of explosion upon piercing the skin after cooking. Chefs do this by 'docking' the skin - poking holes in it with a fork. And when oven baking, the exposed portions of the nail will heat up through conduction (Newton's second law of thermodynamics) and transfer that heat into the inner portions of the potato supposedly cooking the potato quicker. If actually so, it would be negligible at best.
In all my years of professional cooking I have never seen this technique done by a Chef or a prep cook. Most just dock it and bake it. It can leave an unsightly hole and really annoys said tuber.