Simple. An auto-update system. When you turned it on, like let's say in the first Diablo, it would track your progress and automatically distribute skill points accordingly. For example, if you're a brawny fighter it'll put the extra point into Strength. It'll put it into Magic if you use runes, special staves, and reading tomes often. It'll place it into Dexterity if your character likes using bows. Finally, it'll put that point into Vitality if it senses you're taking a beating and drinking Health/Rejuvenation potions and using Scrolls of Healing a lot.
You could turn it off if you liked, and the advanced setup would allow you to select where you want points distributed manually instead of it detecting your playing style.
That's all for now. Sometime soon I may digress something.
Oh, by the way, I got killed by The Butcher today. *sigh* For the fifteenth time in a row. At least he's being fed. *scoffs*