Once you upgrade a weapon to the point where you can't upgrade it any further and it's rarity 8 or above, you will gain the ability to hone the weapon, either adding increased attack power, defense (and a hidden Divine Blessing), or life (which sometimes heals you when you attack).
The amount of health restored through a life hone depends on the motion value of the attack. Weak attacks heal less than strong ones - for example, most attacks by Dual Blades will heal for around a Herb or Potion's worth, whereas a level 3 Great Sword charge will heal more than half of your maximum health!
But how does the life honing work with attacks that hit multiple times, such as a Charge Blade's ultra discharge (which hits 3 times + the number of explosions) or most of a Bow's attacks (almost all of them hit multiple times)? Does it only "proc" on a single part of those attacks or does it use the whole thing? Is the amount healed based on one of these parts or does it take the whole attack into account?