What is the significance of a Scene ending in the Extraction mission?
There are two main purposes to a scene in the game and while what happens when a scene ends varies based on the mission the basics are the same. In the case of an extraction you have a set round limit instead of a number of scenes to complete. In this case the scene end does two things, first is it heals all runners and the client, second is to provide reset of certain abilities. This is in addition to the normal addition of new obstacles. 

Rules


  Most Missions:
  
  Are divided into “Scenes” with small rewards, breaks,
  or changes of play mode between Scenes. Each Mission
  sheet will describe what happens during a Scene
  and when a Scene ends.
  
  Some upgrades are usable once per Scene. Once used
  during a Scene within a Mission, they can’t be used
  again during that same Scene. When a Mission changes
  from one Scene to the next, these abilities become
  available for use again.