Guards are used when two opponents are facing each other in combat. Each is trying to protect against attack while looking for openings and formulating attacks. In a self-defense situation, this is not desired; what give you time to think also give the attacker time to think. In a self-defense situation, the primary actions are either to run away or to strike first before the attacker is prepared. A fight is combat between two people. An ordinary person is not looking for a fight and does not want to be in a fight; he or she wants to protect him or herself, stop the attack, and flee; therefore, a guard is rarely necessary. Thus, the old patterns emphasize active blocks and strikes, not passive guarding. Instead of guarding, the original martial arts emphasized controlling the attacker's limbs to prevent attacks and to provide opportunities for counterattacks. Training emphasized "one strike-one kill;" it did not emphasize standing around fighting until the attacker was convinced to stop the attack, as is taught in "politically correct" martial arts where students are taught to be sensitive to the plight or the attacker.
If a self-defense situation evolves into a fight, then a guard becomes necessary but even then, the major concern should be in controlling limbs and attacking, not waiting for an attack. In a fight, whether it is in competition or in the street, the guard used should be what is best for rules or the situation.
WTF sparring competitors rarely use hand attacks so they do not need to guard against them. Most WTF kicks come from the floor so the foot travels from the floor to the target in a straight line (usually a 45 degree angle of travel). This means that, for most of a kick's travel, the foot and leg are always moving upward, so a low guard may block a middle kick or stop a high kick before it gets to a high target. Practically all WTF sparring is done from a medium to long kicking range that is too far away for effective hand attacks. From this range, a low guard is effective. Since competition sparring rules are used during training class sparring, hand attacks are generally ignored.