My DH reckons you must never, ever cook a raw chicken and potatoes/other veg in a roasting dish as it will at least give you food poisoning if not kill you instantly.
Sounds daft to me...
Take last night, I bought raw 'rotisserie' (basted) style chicken from M&S. Cooking instructions said to roast in its bag and on its tray but I took it out of both, chucked it in a big roasting dish with spuds and garlic, two hours later it was cooked and delicious.
No-one died.