Mostly just a costly drop of new items and buildings for your settlements. If that's not your vibe (and it's certainly not mine), then it's not going to be worth your while. Also allows you to put NPCs of your choice (including your companions) in an arena to battle for your entertainment, which utterly devalues them as characters and effectively makes them action figures for the player to slap together. Fun for YouTube poop shenanigans if you're 12, I guess.