ITF sparring emphasizes using both hand and foot attacks, both separately and in combination. ITF kicks come from a high chamber so the foot starts its forward travel from about belt level. From this location, the kick may travel either level, upward, or downward. The opponent knows a kick is coming but there is no indication of whether the target is low, middle, or high, so the guard must protect all targets. ITF sparring is done from short to medium range so hand attacks are constantly a threat.
During completion, some Taekwondo organizations, such as Taekwondo America, do not allow hand contact to the head but do allow hand fakes to the head. However, during school sparring sessions, they do allow and encourage hand contact to the head. This ensures that students are used to hand attacks to the head, that they keep their guard up at all times, and that they learn to avoid, deflect, or block hand attacks to the head. This means that students are always alert to hand attacks to the head, even during competition. In competition, it is the attacker's responsibility to avoid hand contact to the head.
Overall, it is best to keep the guard high and to stay always alert for hand attacks to the head. This guard is more effective in real fights when you cannot risk letting even one punch reach the head. When the guard is low, you are inviting punches to the head, especially when the opponent has quick hands. As general rule, as the range increases, the guard moves lower and more extended, and, as the range decreases, the guard move higher and closer.