Quote Originally Posted by Skyblade View Post
Once they overstay their welcome, though, it started to irk me. For one thing, it raises the question of why did they stop. In the books, they're used in one battle, and that's it. Their oaths are fulfilled and they can rest. In the movies, they're used in two distinct battles. So why not simply ask them to take out the rest of the forces of Mordor as well? Would three battles really be pushing things so much farther?
I can only answer from my perspective, but I think it was because Tolkien clearly wanted them to not be viewed as a force or an object to wield at the pleasure of their master. They were simply paying a debt in return for their release. I also think that Tolkien was so incredibly affected by war that he would never allow such a thing like an army to be used against their will (whether they were dead or alive matters not) to fight in battle more than necessary. Additionally, Aragorn would never ask for such a thing because he is an honorable soul. That would be my guess.

I see your argument, though. Using them in two battles in the movie did no favors for them, and it does raise questions like, "why not just keep using them?" This is why I get angry when liberties with material are taken, because all it does is raise questions.