Efficiency is a modifier that affects the productivity of a Porco working in a building. A higher efficiency modifier will allow each Porco to do more work, either by working more natural resource tiles, operating more annexes (excluding the Market stand), or processing more raw materials into processed goods at a time.
Efficiency will not cause a building to produce extra goods from input materials, but rather cause the building to consume more input materials to create more goods at the same ratio as before. Likewise, higher efficiency will not increase yields from natural resources or annexes, but rather allow more of them to be operated at full productivity by a single Porco.
Efficiency is primarily affected on each building by building level, and nationwide by economic policies such as Gift economy or Fair Exchange. The effects of each modifier will stack, but certain policies are incompatible with each other.