A lot of people will choose to wrap their potatoes in foil before cooking because they think that it helps to trap in the heat and cook them more quickly and while this might be true, it also helps to steam cook them which means the skin is softer when finished instead of nice and crisp. We like our potatoes to have crispy skin, so we opt to not use foil. If you like a softer potato skin, go ahead and use the foil.