This should be familiar as the tunnel to No Man's Land on the Wizernes map. If people take up firing positions in the red zone, teammates are forced to cross in front of and will block their line of fire. Conversely, if people take up positions in the green zone, enough space is left behind them for teammates to move into No Man's Land without blocking LOF
In this example, we have a three man team moving in a staggered file, each with an assigned zone to watch. Once contact is made, the point man immediately returns fire. The trailing two men, move on line and establish interlocking fires on the two enemy soldiers