Law's attack described by redon
Well, the shock wave that Law creates with his attack runs through the entire sword and ends up coming out of the tip. That is why the impact creates a large hole in the ground of Wanokuni, which is where Law drives the point of his sword.
If instead of pinning it to the floor of Wanokuni, he had pinned it to the floor of the Live Floor where he is fighting Big Mom, the entire island would have been blown up. That is why Law extends the sword until it sticks in a place where the explosion does not affect anyone.