What happens if you don't preheat an oven?

[armedmonkey]

I had always heard that it is the uneven temp inside the oven. Let’s say that you are preheating the oven to 350 degrees. While it is preheating the air in the center may be say, 200 degrees, while the air near the heating coils or burners is much hotter - say 450. The reason is that the coils have to be much hotter than the desired temp in order to bring all that air up to the desired temp. If they just heated up to 350, it would take forever to preheat. So if the food (or any part of it) is near the heating elements it is cooking at too high a temperature and will burn.

[Arnold_Winkelried]

From How Stuff Works:

This, by the way, is why you pre-heat an oven. The idea is to get all of the air in the oven up to the proper temperature so that the burner does not have to come on very often or for very long. That keeps the infrared radiation from the burner to a minimum. That also explains why only the lower burner comes on during baking – the radiation that does get generated by the burner hits the pan rather than the top of the cake.

[susan]

I just cooked a Swanson Hungry Man dinner without preheating the oven, and it was still done in 40 minutes. I find most food is fine with a cold start, other than the baked items elaborated above.