Anytime you boil something or cook something in water, some nutrients get transfered in to the water and out of the food. This is why some people use the water and make a soup or stew with it, at least, it was commonly done in the old days. It made for some good, hardy soups etc.
That said, I wouldn't cook a chicken over night. It doesn't cook the same as red meat and pork. The difference is, red meat and pork can be slow cooked to a very low temp, where as chicken needs to reach a higher temp and slow cooking it really slow just doenst yield the same return. What size is this chicken? THe ONLY time I would consider cooking over night if it was a big ass Turkey, and we are talking about 30lbs.