Logic versus random

In versus mode, this entity is used to keep Left 4 Dead's random nature more consistent between the two rounds. Something such as the location of a powerful gun could affect how well a team does, in which case, the other team should have that same advantage/disadvantage during the second round.

Some argue that these advantages are marginal, and keeping these things consistent between rounds can make the game even more unfair, due to players being allowed/forced to plan a strategy involving those "random" events in the second round, when they could not in the first. In any case, Valve did not use this entity with any apparent consistency, so using it isn't something players expect out of a campaign.