Swap the performer, keep the performance.
Feed it one video and a few reference images of your character, and the person in the footage is replaced while the shot itself stays exactly as it was — same camera move, same lighting, same background, same timing, same audio. That makes it useful for recasting a scene without reshooting it, putting your own OC or a designed character into existing footage, building a consistent cast across a series, dubbing and localizing content for a different market, or standing in for a performer in stunt and body-double work. Concept artists can use it for previs, marketers can swap a model without booking a new shoot, and anyone with a character sheet can see that character actually act.