what does it do?

Changes the base of the item to the next tier higher.

can possibly raise the defense but remember when u reroll an item like that u reset the base defense...
like on hoz u can possibly gain 0 defense haha but increase the str req
on the other hand for a non eth u could also jack the def up like 180 or so i forget exactly how much is perf up roll

higher smite dmg

defense # is for ocd jsp nerds. fuck that shit doesn't really make a big difference in the char at allt