If the essence of drama is conflict, it stands to reason that it will only ramp up with the size of the cast. The addition of new characters to a story can create new issues and spur the development of the leads, or cause readers to invest in a new personality that might become a fan favorite. However, some writers take things way too far.
The key to managing any cast of characters is balance. True supporting characters (I’m not talking one-scene walk-ons here) need to contribute something to the story regularly unless there is some overriding reason for them to leave (death, a major fight with the lead, etc.). In longer series, supporting characters often simply … vanish.
Webcomics (as much as I love them) are the poster child for this practice. Frequently, the writer starts out with a core cast of characters he or she takes the time to develop. While there’s a lead, he or she interacts with everyone else much as a real person would with actual friends. The relationships feel natural because these people actually spend time together. Unfortunately, as things draw on, a lot of writers seem to burn out on their own creations. Slowly, the supporting characters come to occupy their own side storylines. And when these plots conclude, the characters vanish for inordinately long stretches of time, if they ever come back at all (and even then, it’s usually little more than a cameo). Not only is this kind of writing a slap in the face to readers who were invested in these characters, it leaves them hesitant to care about anyone else for fear of the same thing happening again.
But just as there’s an issue with too little face time, there’s a problem with oversaturation. Working with characters and their relationships always amounts to a juggling act. Each new character is the equivalent of a new bowling pin being thrown up in the air. And no matter how talented the performer, one too many objects will cause all the others to fall. Personal histories inform personalities and interactions, and the more characters an author adds, the easier it is to write them inconsistently or overcrowd a story to the point where it becomes meandering. So much so that the whole intent of a story can get muddled, and sometimes, even the lead.
A good writer always needs to keep the characters he’s writing in mind. Best friends don’t usually walk out of each other’s lives without explanation, nor do most people have the same dozen or so individuals traipsing through their personal lives each day. Just remember, a reader needs a focus, and it’s difficult to get a good look at anything when there’s a giant crowd in front of it.