The performance challenge exists because of various set operations made for each ray of light. Only recently could our personal devices (laptops) handle this technique.
Photorealism is the ultimate aim here, and rendering engines such as Unreal Engine are built to provide realistic renderings for games.
While ray tracing is used for calculating realistic lighting and shadows in an environment, it can also be used for first person shooters in video games.
When bullets travel quickly through the air, a ray of light is simulated to check if a person is targeted directly or not.