Fallout 4 introduces us to all kinds of interesting and unique companions. Upon reaching maximum affinity with a companion then you will unlock that companion’s perk. Perks are permanent buffs that stay active once unlocked, regardless of whether you use the companion or not. Here is a list of all currently known companion perks (this will be updated once Fallout 4 is released).
Your action points regenerate faster if you are below 25% health.
+10 damage resistance from damage dealt to you by all robot sources.
Heals you by 100 points if your health is reduced below 10%. Only works once per day.
You deal +20% damage against Ferals, Super Mutants and Synths.
Upon reaching 250 rads or higher you will get criticals 20% faster.
Headshots in V.A.T.S increased by 20%.
An extra guess when hacking and terminals cooldown 50% faster.
+100% xp bonus from speech challenges and finding new locations.
Deal +20% damage and gain +20 damage resistance when against 3 or more enemies.
When below 25% health you deal 20% more damage with melee weapons.
+20 damage resistance vs. energy damage.
Anything else to add?
Try your best to keep your companions happy and you will be rewarded with some very powerful (and permanent) bonuses.
If you have any other information about the various perks then comment below and share it.