"We avoid the frontal and advance from the side, seizing changing conditions." Yang Family Manuscripts Collected by Li Ying-ang, quoted in T'ai-chi Touchstones: Yang Family Secret Transmissions, compiled and trans. by Douglas Wile, p. 37.
"We must quickly evade by withdrawing our center and attacking from the side." Transmissions of Yang Pan-hou published by We Meng-hsia, quoted in T'ai-chi Touchstones, compiled and trans. by Douglas Wile, p. 67.
This is the meaning of the patterns of Goju-ryu kata. We should study all of the turns and direction changes in order to learn how to "avoid the frontal and advance from the side." This is the structure and lesson of the directions in Goju kata. So often, students (and teachers) looking to apply the techniques of kata look only at the hands. It's as if we're lions caught in a cage at the circus and the only thing we can focus on is the chair held in our face. The initial movement in kata--the "uke" or receiving technique in a series--is usually accompanied b the movement, generally off line, of the feet and body. We move in along a northwest or northeast line (supposing that the kata starts facing north) as in the kicking techniques of Saifa or the first three shiko dachi stances of Seiunchin. We step to the side (the attack coming from the west) at the end of Saifa. We step back along a southwest or southeast diagonal at the beginning of Kururunfa. But so often, people either ignore the stepping or directions of kata or they will argue such nonsense as "the kata shows stepping forward but in actuality one would step back" (as I've heard quite reputable people say about the opening moves of Seiunchin). The kata is a teaching device. If you study this one lesson carefully, you will see all sorts of useful things that may not have been apparent before.
Of course you first have to see where the sequence begins, where the initial "uke" or receiving technique occurs. But once you have found these, you have to keep in mind that the kata itself, at least with Goju-ryu, is showing how to "avoid the frontal and advance from the side." The end of Seisan turns back to the front with a right block and left open-hand palm strike. This is a clear example of the kata pattern showing us how to apply this technique by moving to the side, avoiding the attack, removing our center, and attacking the opponent from the side, placing ourselves in a position that is at once safer and from which we are better able to control the attacker. So often those who merely look at the hands and ignore the lessons contained within the kata's pattern simply turn to face a new opponent, one attacking from the kata's original front, in this technique from Seisan. If you imagine that the attacker is really advancing from the east (the right) then a very different understanding of these techniques may emerge.