Leaving your meat out to eat the room temperature before cooking is an essential part of cooking a really juicy cut especially in larger cuts of meat like a prime rib. The basic logic behind it is that your meat will reach the desired internal temperature right at its center faster if it starts off the cooking process at a higher temperature. This means that you can achieve the perfect level of doneness that you are aiming for without the meat on the outside becoming dry and overcooked. Taking precautions like this means that you'll get a juicier result with a perfectly caramelised outside and a mouth-watering centre. Please note that the meat must only be let out for as long as it takes to come to the room temperature and no longer as this will cause harmful bacteria growth.