Channel Smite (Combat)
You can channel your divine energy through a melee weapon you wield.
Prerequisite: Channel energy class feature.
Benefit: Before you make a melee attack roll, you can choose to spend one use of your channel energy ability as a swift action. If you channel positive energy and you hit an undead creature, that creature takes an amount of additional damage equal to the damage dealt by your channel positive energy ability. If you channel negative energy and you hit a living creature, that creature takes an amount of additional damage equal to the damage dealt by your channel negative energy ability. Your target can make a Will save, as normal, to halve this additional damage. If your attack misses, the channel energy ability is still expended with no effect.
Since this ability requires that you hit the target should it not negate the will save as do most spells and abilities that require to hit roll?
And since this ability is somewhat like a touch spell should the "charge" not be held when you miss?
Paladin Lay on Hands: Standard Action; Melee Touch; No save; 1d6 damage per 2 levels (10d6 at level 20th).
Paladin Channel Positive Energy: 2 uses of Lay on Hands; Standard Action; Will Save for Half; 1d6+1d6/2 levels damage (10d6 at level 20th)
Paladin with Channel Smite: 2 uses of Lay on Hands; Part of an Attack Action; Will Save for Half; 1d6+1d6/2 levels damage (10d6 at level 20th) + Weapon Damage.
So the benefit of the feat is allowing your Paladin/Cleric to burst his damage without giving up the melee attack(s). This should be useful when fighting a tough/boss undead, combined with smite evil. I think this is a situation that does not happen so often, so the feat is rather useless. That said, a Paladin could really finish that encounter he alone.
The feat maybe could be useful for a negative chaneller who also focus on melee attacks, as the living bosses should be more frecuent than undead ones. It also helps if you don't have Selective Channeling or enough Charisma (or your group is big).
It could be great for evil cleric NPCs. Imagine an ancounter versus 6 level clerics with Extra Channel and Channel Smite.