alea iacta est
If you've played Final Fantasy VI, then you don't need me to tell you that the Floating Continent is the major turning point of the game. The World of Balance, while fraught with political struggle and violence, is a beautiful place to live. After the events unfold on the Floating Continent, the World of Balance is transformed into the World of Ruin, a bleak and dismal replacement. Most of the lush forestry is transformed into desolate land, and its occupants are psychologically effected by this transformation (not to mention the general destruction that took place during this transformation).
Even though the World of Ruin is horrible in comparison to the World of Balance, simply put, it is better than no world at all, and everyone living in the World of Ruin has Shadow to thank for preserving a place for them to live. Even though the main party is more consistently motivated to stop Kefka's destruction of the world, Shadow is the one who ultimately saves the day. Just when your party thinks nothing can be done, Shadow enters the scene as a distraction to Kefka, and he is able to not only thwart his plans, but save your party in the process:
Kefka: Who're you?! (Shadow rescues Celes and pins Kefka between the statues)
Kefka: Nooo! (The bound party members are freed)
Shadow: Go! There are people counting on you! (The statues' balance is destroyed)
Shadow: Don't worry about me! Run!! I can't stop this chain reaction! I'll see you again. Count on it!
Kefka: You can't escape me!! (Kefka sends a light over to the far right of the Floating Continent)
Shadow...... Get outta here on the double!
While Kefka had pinned the party into a corner and was at a position of advantage, Shadow's unexpected entrance not only freed the party, but it distracted Kefka enough to prevent him from causing more destruction. Not only that, but Shadow stays behind to ensure that Kefka is not able to catch up to the party and cause more trouble. With only seconds remaining before the destruction of the Floating Continent, Shadow arrives at the Blackjack and takes off with your party.
One of the most interesting parts of this scenario is the fact that the player has a choice to make: you can either wait for Shadow, or you can leave him behind. If you leave him behind, he dies and you are unable to recruit him in the World of Ruin. Shadow is the only character in the game who you can optionally kill, and I feel like that gives him an extra bit of depth. It is ultimately up to the player if Shadow is to become a martyr or an undercover hero. If you do decide to save Shadow, you will never hear him talk about the events on the Floating Continent again -- he never tries to take credit for his heroic act, and it's not entirely clear that he recognizes that it was a heroic act. Whether Shadow likes it or not, he managed to save the day, and there are a lot of people who would have died if he had not done so. And in the end, the World of Ruin is not so bad -- by the end of the game, we see glimpses of the towns being restored to their previous conditions. Shadow may have branded himself as the outcast of the group, but his role in brining peace to the world is no smaller than any of the other characters'.