Rook Island is under the control of Vaas’s pirates and the outposts are their strongholds—key strategic positions that the pirates use to subjugate the native islanders.
When Jason captures an outpost, he frees it from the pirates’ control, allowing the Rakyat warriors to move in and claim the area as their own. The world becomes friendlier, the roads become safer to travel, and the island more conducive to exploration. This change brings Jason new opportunities on the island. New activities, challenges, and side quests become available. New safe houses, shops, and fast-travel points are unlocked. Outposts really give the player agency—the opportunity to have a real impact on the island. – Mark Thompson, Lead Level Designer