I'm the opposite of Horns. I worry about the chicken being over, rather than under, cooked so I worry that the juices running clear will take me further than optimal cooking. I use a thermometer and take it out lower than would be suggested, then give it a nice, long rest. At least that is my current thinking, since 9/10 times I just check to see if the juices are clear, though usually by pricking the thing than using the cavity. I don't know if that gives a different result, it is just how I learned.