Re: crushing blow?
The most important reason to use smite is that it bypasses blocking. While you can increase your ar or level to improve your chance to hit, there's nothing you can do to avoid your attacks being blocked, except for using attacks which always hit. CB will help a lot to kill hell Baal and Übers and it's not capped at 50%, like static field.
CB deals only a fraction of a monster's remaining life and you cannot leech from CB damage, so dealing a certain amount of regular damage is still important, for gaining back life and dealing the last tiny bit of damage to kill the enemy.
CB only works together with melee and missile attacks which deal physical damage and not with spell-like skills like hurricane. I'm not sure if CB works together with berserk (barb skill which deals magical damage), that skill is somehow a special case, as the magical damage gets boosted by off-weapon %ed, in contrast to the elemental part of e.g. vengeance (paladin skill).