Well, it gives the movie or the story a deeper meaning. Since it's based on a true story, it can inspire people more. It shows the strong bond between humans and dogs, and how a dog's love for its owner can drive it to overcome so many difficulties. This real - life basis also allows viewers or readers to connect more easily with the emotions in the story.
The significance is that it makes the story more touching and believable. It shows that such amazing loyalty and the journey of a dog can actually happen in real life.