You can't cook raw potatoes at as high a temperature as you can previously cooked potatoes. If you did, the outside of the potato pieces would be burnt before the interior was properly cooked. This problem doesn't exist for leftover potatoes because their interiors don't need cooking. The advantage of pan-frying potatoes at a fairly high heat is to minimize the development of a sticky film of starch on the surface of the potatoes. This substance can cause the individual potato pieces to stick to the pan and break apart when you try to dislodge them.
** Asian Recipes