No, preheating is for the oven temperature to reach the set temperature, which is convenient for calculating the time.

For example, if a pizza is baked for 20 minutes, you put it in without preheating it for 20 minutes. It's cold, and it takes 7 or 8 minutes for the oven to reach 200 degrees, which is equivalent to pizza 13 minutes. It must be undercooked.