First, using aluminum foil is fine, and has numerous foodservice applications. What we say about foil is, avoid using as a wrap when baking potatoes, as foil will prevent moisture from the potato to escape during cooking. This will cause the interior of the potato to be less dry and fluffy (desirable trait) and more of a gummy-texture (less desirable). So, avoid wrapping potatoes in foil when baking. Some restaurants will opt to serve the unwrapped, baked potato in a foil jacket when plating for aesthetic reasons, which is perfectly fine. In any preparation method, the potato skin is good to eat if preferred, and if so, provides added nutrients and fiber to the meal.