In many ways, the minor character is sometimes easily forgotten. The gregarious taxi driver, the helpful woman at the store, the nosy coworker, and the grumpy neighbor all have their parts to play, but the reader tends to not give much thought to these brief appearances. So why incorporate them at all?
I think it’s not hard to understand that the reader’s experience of a novel and the author’s experience while writing it differ quite a bit. One thing that the average reader may not realize is that no character appears in a story without a distinct purpose. Any novelist worth his or her salt will pay exacting attention to every facet of the novel, including the minor characters. There must be a reason for a particular character to appear in the narrative, and the presentation of that character must maintain a balance that is consistent with his or her importance to the action and development of the story.
In The Truth Seekers, Mrs. Olivia MacDonald serves as the necessary chaperone for her young friend, and so must be blended into the scenes in which she appears. She herself is not a major player, and her voice must not be allowed to overshadow those of the main characters. However, at certain points her actions move the narrative forward, so we need to see enough of her to have a sense of who she is as a person. By way of contrast, the existence of the male lead’s friend John needs to be established, but we don’t need to interact with him a great deal.
In Wishing Cotton, Olive meets Mr. J.P. Croupington (“Pinger” to his friends). This character’s importance begins and ends with the scene in which he appears. So why have him at all? He helps to provide comic relief, but his conversation with Olive also works to create the mood needed for Olive’s subsequent conversation with her friend Blair. So old Pinger provides a necessary element to the narrative, but once his usefulness is at an end, he vanishes from our view.
In the case of quiet John mentioned above, a good deal of his lines were cut in order to achieve the proper balance. Every time a character is introduced into the story, their voice, opinions, and personality are also inserted. The people they are influences the main characters on some level, but their appearance must blend into the story. In other words, it is one thing to have the gregarious taxi driver chat with the main character and give a suggestion that impacts that character’s choice of destination. It is another thing altogether to allow the driver to take center stage. We don't need to see the color of his eyes or have his life story laid out for us. A character that has such a limited part to play cannot be allowed overshadow the main characters.
All the same, minor characters are important, and often the author is able to provide gorgeous characterizations that give the reader a firm grasp on the minor character before he or she walks offstage. When the right balance is present, the minor character can be one of the most vital elements in a novel.