Some studies listed by Wikipedia claim that peacocks with smaller tails suffer more predation (mechanism unknown),

A predator which relies on vision for target identification might survivably assume that anything which appears large and flashy actually is physically large, with muscles and defenses to match, thus out of it's league, and look elsewhere for prey. A wide flat tail with a colorful pattern is probably the most cost-effective way to maximize your apparent size, at least from the front and back.