Using Smite upon the Ancient Krug will grant you Gift of Heavy Hands for 90 seconds, causing every 6th basic attack to stun minions and monsters. Additionally, you can attack a tower to expend the buff early - dealing a large amount of bonus true damage (65 + 15 x level). This bonus can only be claimed once per spawn, and only by smiting the Ancient Krug - Smite cannot be used on the small Krug.

Usage:

First 1-2 jungle clears for autoattack based jungle champions, which often includes even tanks like Nautilus who typically run Attack Speed Marks if not Quintessences.

For someone like Fiddlesticks who does most of their clearing with abilities, picking up this buff makes no sense.

After your first clear or two you should save your Smite for champions or more useful buffs such as Razor Sharp from the Raptors unless you happen to be on your way to push down a tower and the pathing makes sense (the buff only lasts 90 seconds, so keep that in mind if your objective is say the inner top tower, which is on the opposite side of the map from the Krugs...of course if the enemies' Krugs are up while you are over there and you want to take the tower, you know what to do).

And a question that popped into my head this morning, that I don't seem to readily be able to find an answer to, is whether or not the bonus damage to turrets applies to the turrets that Azir can create via his passive Shurima's Legacy?