It's common to include a large number of people in a hiring decision. When handled properly, you can reduce your risk of making a hiring mistake by getting valuable input from a variety of perspectives. But when your hiring process is not organized properly, you will only be wasting everyone's time by including more people.
One of the most common dangers in the hiring process is "groupthink" -- where the opinion of one vocal (often powerful) interviewer dominates the narrative about a candidate. When the vocal participant expresses an opinion, everyone with a less firmly-held opinion usually agrees. (The research on groupthink is quite compelling: check out How Certainty Transforms Persuasion in the Harvard Business Review.)