Once the Exit Gates are powered, No One Left Behind activates:

Increases your Unhooking and Healing speed by 30/40/50 percent.
Grants 50/75/100 percent bonus Bloodpoints for actions in the Altruism Category.
Grants the unhooked Survivor a 7 percent Haste Status Effect for 10 seconds.
The Auras of all other Survivors are revealed to you.

Unlocks potential in your Aura-reading ability:
While you are hooked:

The Auras of all Survivors are revealed to one another.
Whenever the Killer is within 8/12/16 metres of your Hook, their Aura is revealed to all Survivors.
While any other Survivor is hooked:

The Auras of all other Survivors are revealed to you.
Whenever the Killer is within 8/12/16 metres of the hooked Survivor, their Aura is revealed to you.

In your countless years in The Fog, you have seen it all, and when you are focused, you can remember most of it too. Succeeding a Great Skill Check while repairing a Generator reveals the Killers Aura to you for 4/5/6 seconds.

Increases the Success zone of Great Skill Checks while Repairing and Healing by 10/20/30 percent when in the Injured State.