How does S.P.E.C.I.A.L affect settlers in Fallout 4?

I can give special raising gear to my settlers and companions and it increases their stats but I have no idea if it gives them any useful benefits.

I know Strength increases companions carry weight and (hopefully) raises their melee damage.

But what about Agility or Perception? Do they have any effect on weapon accuracy if npcs don't have access to vats and don't use action points (melee settlers probably use action points for power attacks similar to Skyrim).

I did some research and can now answer your question. Strength does raise damage, Agility increases attack speed and defence, And perception raises accuracy. Yes they have an effect on accuracy if they don't have access to vats and don't use action points.