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.

When you unhook a Survivor, the rescued Survivor benefits from the following effects for 4/6/8 seconds:

Scratch Marks and Pools of Blood are suppressed.
Additional 7 percent Haste Status Effect, boosting their Movement speed.
Guardian reveals the Killers Aura to you for 8 seconds.

Suppresses both the Loud Noise Notification and the sound effects triggered by rushing to vault Windows, Pallets, or rushing to enter or exit Lockers.
Quick & Quiet has a cool-down of 30/25/20 seconds.

When another Survivor loses a Health State within 32 metres of your location while you are in the Injured State, you benefit from the following effect:

Grants 40/45/50 percent of your missing Healing Progression to your Health Bar.