Big Quiver is a gear perk that raises how many arrows you can carry. It is a must if you use bows as your main weapon for stealth or hunting.
Your arrow reserve goes up, so you can stay on a bow for a whole base clear or hunt without running dry.
Wear one of the gear pieces that carry it: Kheshig Livery, Primal Pants. Each piece only takes one body slot, so plan around the other perks you want.
Yes for bow users. If you never use a bow, this perk does nothing for you.