I just received my new oven! Unfortunately, it is a little too small, so I have to send it back and wait for the next one. I did notice, however, that this oven has a separate temperature control for each heating element, upper and lower. That sounds really cool to me but I don't know how to use it. When would I want to use a lower temp at either the top or bottom? Would cooking pizza benefit - having the upper temp lower than the lower temp?