Growing up in a pizza family, we always had pizza in the house and it could be eaten at any time as it seemed to be in constant rotation. In with a new one and out with the old. We never threw it in the fridge as it was in rotation and always eaten so we just threw the box in the oven. More than anything, it was put away as a tidying measure. Growing up we knew it was in there and it was never a problem. It was really second nature to just take it out when it was time to cook. I don't know if my cousins and the rest of the clan did this, but I know we did in my house.
I'm certain this was not the case for others and I learned this when I first moved to NYC. My brother and I were living in Brooklyn and our roommate Melissa panicked one day when she was pre-heating the oven. Yep, she was not in the know of how we do/did things and had no idea why the oven had smoke billowing out of it. Pizza Box.
Understanding that it was probably easier to reprogram myself than to instruct those around me, I stopped putting boxes (of any sort) in the oven.
Cut to a more modern me with a love of cooking and a Manhattan apartment and you see that the relationship of appliances/pans and cabinet space is not a direct one. Way less space and more shit equals me storing pots and pans and other stuff in the oven.
(Though I realize it's already too late) I'll make a long story short and say that I had the oven at 475° and was ready to throw in a meal to be cooked and realized I had about 15 things in there that were ready to burn their way through me. It was like they were taunting me. Luckily I kept it together and didn't get mad while I found my way through a balancing act and creative counter space usage without burning myself nor blowing a gasket. Unfortunately it was a delayed reaction 'cause while I write this, I'm getting pissed off.
Long and short of this tip: Check your oven before you heat it.