Prior to being nerfed, dropping a dragon egg in a lazy chunk would break bedrock. This was the simplest way of doing so and often the reason for mass duplication the egg as it made clearing the top four layers of bedrock inside a spawnproofed perimeter a reasonable (if still quite daunting) project.
[Or the 0-layer as well, although this would lose an egg for each location cleared, but allowed the most efficient spawning in farms.]
