luck improves a variety of things in 8 it increses your chance to devour a enemy (hence I have a high luck stat) and it reduces the chance of a status effect working 255 luck is rather like having 50% resistance on all status's + ensuna = a rough 70% defence rate against status. The higher your luck the less a one hit kill move will hit you too. Chocobo forest (bit of guess work) might be affected by the luck stat as well. Finding rare items is also affected by luck stat it's useful also speed and evasion go up (a little a very little) with the luck stat