Many a Sci-Fi story is written around the premise that the future is so bad that the time traveler goes back in time to change the history - at any cost, including his own existence. Terminator movies are just one example.
This, however, creates a paradox: if the time cop gets destroyed in the process of changing the past then who changed that past in the first place? One answer to that paradox is the concept of the fractal Multiverse where Universes copy themselves whenever a tiniest event takes place. One obvious question about that theory is that you can't copy a Universe without having an equivalent amount of energy or mass at hand.
The way we solve this conundrum is by using Time Cops from different dimensions to police our own home dimension. Therefore, if I accidentally shoot my Super-star martial arts actor counterpart, it wouldn’t be that big of a deal.