The Significance of the Interview Format of World War Z

The novel World War Z is structured as an oral history, in which dozens of survivors of a zombie apocalypse are interviewed on their experiences. The interview format is one of the most striking things about the novel, and what sets it apart from other zombie apocalypse stories.
How does this structure change the readers' perception of events? What role does the unnamed and uncharacterized narrator play? If the novel were kept the same but followed a single character, possibly with flashbacks to other events, would our perception of the world change? What does this wide range of stories bring to the novel, and how do the separate interviews still form an overarching story arc?