The turkey comes out moist and golden - with no effort on your part. Slow-roasting keeps the juices in. It is nearly impossible to over-bake, because the temperature is so low. The secret is NOT basting or salting. Basting or salting draws out moisture and dries out the turkey.
IMPORTANT: Plan ahead: Thaw turkey in refrigerator for 1 day per 4-5 lbs, (For faster thawing, you could thaw in cold water. Change the water frequently.)
Allow 1 hour per lb + 1 hour to cook - i.e. total: 21 hours for 20-lb turkey.