There is actually less to ’xkill’. It nukes the X window from orbit in a very violent manner. The owning process(-tree) will usually just instantly curl up and die.

The main benefit is that it doesn’t actually kill the process, it only nukes the window. As such, you can get rid of windows belonging to otherwise unkillable processes (zombies, etc).

Also, it’s fun. Just don’t miss the window and accidentally kill your WM. (Beat that Wayland)