I didn't know this - thank you! My character finds herself overwhelmed by large groups of tough enemies - she fought five or so Skeleton Heroes today. She can deal with them with about three blasts of her custom destruction spell, but she doesn't have enough magicka to do so for more than one enemy. I'll have to put more into luck!
Just so you know that it only works on your custom spells. Only. And adding points to Luck every level is quite costly, basically making you be more squishy. Most of my mages will use one of their two attributes and give it to Luck as an emphasis.