Smite's not just for Junglers, anymore.

Look at everything Smite now brings to the table for a champion. Remembering that Smite is very spammable, the possibilities of what any champion can do with it (now that there are so many upgrades it gets from the machete item tree) is rather enticing. Early-mid game, it would help a ton with leashing (and getting the Smite buff in the process), be something to finish off a difficult creep, or maybe even have a bigger chance at stealing the enemy buff if invading. By late game, when you have finished building the machete item tree and have given it the enchantment, it turns Smite into a very spammable version of Exhaust/Ignite while still keeping in mind that you can get lots of awesome buffs from using it on Jungle creeps.

Long story short, it would be risk-reward choice that makes late game very rewarding for those who were able to keep up with an enemy team that consists of "normal" summoner spells.