From what I understand, eating to satiety, even when it results in a caloric deficit, is fine, because the body is calling the shots, but eating to a predetermined caloric intake runs the risk of putting the body in famine mode. As we lose excess body fat, of course, our appetite increases, until our daily energy expenditure is met completely from food intake, because there is no more excess fat to burn off.
There is a point in the starvation process where the body will start cannibalizing lean tissue in order to hold on to its fat store as long as possible. Of course, eventually the fat does go, but when that happens, death is not far off.