Source: Player's Handbook
You can cast spells to maximum effect.
Benefit: All variable, numeric effects of a maximized spell are maximized. A maximized spell deals maximum damage, cures the maximum number of hit points, affects the maximum number of targets, etc., as appropriate. For example, a maximized fireball deals 6 points of damage per caster level (up to 60 points of damage). Saving throws and opposed rolls (such as the one you make when you cast dispel magic) are not affected. Spells without random variables are not affected. A maximized spell uses up a spell slot three levels higher than the spell's actual level.
An empowered, maximized spell gains the separate benefits of each feat: the maximum result plus one-half the normally rolled result.