The Loop Kill is a loop with a total focus on speed. It is almost considered a Smash though smashes often have little topspin. When you need to generate speed, the loop kill is the best shot.
Since it has less topspin than a regular loop or a Loop Drive, the ball doesn't arc down toward the table as much, so you'll need more accuracy. It is safest when the ball is higher as it will be easier to land it on the table.
These are sub-pages of the Loop Kill page (a child in the hiararchy).