I think this single move has a really important role in the story.
My theory is that Imu is actually over 800 years old. He is the one that United the original 20 kings under the World Government. And someone used Perennial Youth Operation on him. And I don't think Law is gonna live long. He might actually use it. And if he does, it probably be on Luffy if he's at death's door. No way to save him after a world-shaking battle, probably against Blackbeard, Akainu, Kaido/Big Mom or Imu. In the case of Big Mom/Kaido, they flatten Law and Luffy, both of them at death's door, Law sacrifices himself for Wano, Luffy and the rest of the world. Law's sacrifice would skyrocket Luffy's strength and endurance. Which turns the tables and Straw Hats came out victorious.
What do say?