When a pizzeria opens at 10 AM, it doesn't mean that all the employees just arrived shortly before then. Some arrived a couple of hours earlier JUST TO TURN THE OVEN ON, so it can pre-heat to the correct baking temperature (assuming it's a gas oven). The high heat is a requirement. Otherwise, you get less than spectacular results: a longer bake time, the crust doesn't brown enough, or it may develop a tougher texture than normal.
