Please answer now about martial arts visualizing mental training ?

i was looking up on the internet of visualizing in martial arts i say this thing about an olympic karate team scoring most spar points by visualizing and how visualizing has a huge affect some call this mental training so i want to know how it works and have you ever done it , if so did it work? is it a shadow sparring thing or a meditation just wondering since i hear other elite athletes doing it even runners do the visualizing techniques to burn calories so whats the wonders of mystery does it benefit it martial arts to stay calm in sparring and real life situations? please explain