It implies a sense of finality and closure, suggesting that the most important or exciting part of the story has already been told.
Here are some ways it's used:
* To summarize a long story: "They met, fell in love, got married... the rest is history."
* To transition to a well-known event: "He made the winning shot, and the rest is history."
* To dismiss the less interesting details: "They fought a long, hard battle, but the rest is history."
Essentially, it's a way to say that the story has reached its climax and the outcome is already known.