Although Rogue One: A Star Wars Story can be enjoyed as a self-contained adventure, it's much more enjoyable when you take into account how it sets up the very first Star Wars movie, A New Hope, and not just with Jyn Erso and her Rebel team stealing the Death Star plans. For instance, there were numerous cameos from established Star Wars characters, from Darth Vader to Red Leader. Princess Leia Organa was one of Rogue One's more surprising appearances, mainly because viewers weren't expecting her to show up at the Battle of Scarif. As it turns out, we can thank a simple detour for her involvement in that climactic conflict.
While appearing on the most recent episode of The Star Wars Show with fellow Lucasfilm Story Group members Leland Chee and Matt Martin, Pablo Hidalgo talked about how the original plan in Rogue One was for Leia to go straight to Tatooine, but when the Battle of Scarif began, her escort's priorities changed. Hidalgo explained:
The plan was always that Leia was going to go to Tatooine to pick up Obi-Wan and Raddus was going to escort her. Then the news of Scarif came in, and that was deemed more important ... [because] it's the one warship that they have at this point.
After the Rebel Alliance Council officially decided not to follow through with Jyn Erso's plan to steal the Death Star schematics, Leia's father, Senator Bail Organa, told Mon Mothma that he would send his daughter to retrieve Obi-Wan Kenobi from hiding. Had things progressed normally, Leia would have made it to the desert planet uninterrupted and fetched the Jedi Master, but thanks to Jyn Erso and her like-minded allies, chaos erupted on Scarif. As Pablo Hidalgo revealed, rather than continue on to Tatooine, Admiral Raddus decided to take his ship, The Profundity, over to the Imperial stronghold, and Leia and her Tantive IV crew were dragged along for the ride.
In the end, that proved to be an excellent decision. While Raddus' ship was eventually disabled and boarded by Darth Vader, some of the Rebel troops aboard were able to take the Death Star plans transmitted from Scarif's surface and get them onto the Tantive IV before the Sith Lord seized them back. If Leia had gone to Tatooine by herself, sure she could still have fetched Obi-Wan Kenobi, but then the Rebels wouldn't have successfully gotten the Death Star plans away. Granted, Leia was soon captured after her escape from Scarif, but at least by then she had passed the plans to R2-D2, thus kicking off the events of A New Hope. None of this went as planned, but in the end, it was a success.
Rogue One: A Star Wars Story is still playing in theaters, and it is rumored for a home media release sometime this April.