Killing off characters is fun (for writers, not readers). But there's a limit; if you take out certain cast members, you end up crossing a line. So maintaining a kill list will help you from eliminating someone you might need down the line in book 5.
The antihero as a protagonist has gained in popularity in recent years, replacing the typical "always good" protagonists of the past. The comic book genre has embraced the antihero the best, but fiction is quickly closing the gap. So what, exactly, is an anithero?