Gun Nut Perk question

Could someone explain how this perk, and the other mod perks work. When I can already attach 1 mod to a weapon anyways?

HI. Perks that deal with Mods are only needed if you are using a Settlement. If playing Narrative Mode without using a Settlement, you don’t need those Perks and can attach 1 Mod maximum per weapon/item as usual.

In Settlement mode, you need the Perks to allow you to attach the appropriate Mods (page 24 of the Campaign Handbook) and they also give you a free Workbench/Station of the appropriate type which lets you to draw 1 appropriate Mod.