I think that he uses them to show that even one person can make a difference -for good or evil. One small choice can be the difference between life and death, in the case of this book.
Many people say that "it only takes one person to make a difference." Tolkien used that. One minor character helped them on part of their quest. One "minor" character told them an important piece of information. One person gave them food, or shelter. That makes them major characters, in my opinion. True, not the characters that our story focuses on, but major in the way that they influenced the outcome.
Ok, I'm starting to repeat other posts now. So I'll leave it at that!
