Spawn eggs are special eggs that you throw and will hatch an animal. Most of the eggs that spawn animals in creative,but it can't spawn an orca because of it is rare. There's a lot of egg (total 34) that will spawn animals but 4 extra eggs are cooked animal eggs (not counting the I orca). Eggs are useful, even the 4 extra eggs. The 4 extra eggs are useful for eating while the rest are for spawning. You can't spawn all the eggs at one world because it will just say "Too Many Creatures". Birds will drop eggs in survival, which when thrown, will have a certain chance of spawning another bird of that species.