“副本”究竟是个什么东西？

Instances were first proposed by Richard Garriott in the late 1990s as a way to solve a set of related problems which had become obvious in Ultima Online. The problem is simple to state: everyone wants to be "The Hero" and slay "The Monster", rescue "The Princess" and obtain "The Magic Sword". When there are 2,000 and more players all playing the same game, clearly not everyone can be the hero. The problem of everyone wanting to kill the same monster and gain the best treasure was terribly obvious in the game EverQuest. The creation of instances largely solves this set of problems. There are few examples of boss camping and kill stealing in World of Warcraft - because a copy of the dungeon (instance) is always created on demand for you or your party.

FROM WIKI