Factions can go from -3 (at war) to +3 (they’re your allies!), but there’s not much mechanical weight behind it other than special rules for being at war, and an Entanglement that triggers if you’re +3 with anyone.
But what else are you doing, mechanically speaking?
So far in my game, I’ve kept a fiction-first approach. If they alter dice rolls at all, I just treat them as a +/-1 no matter what the rating. My thinking is that, as a narrative-structure perspective, I want to model allies’/enemies’ involvement, but I don’t want that to overshadow party actions. That said, I might use the absolute value of the relationship as the fortune roll pool if I want to determine the severity of the aid/hindrance sent their way.
Does this track with the spirit of the game? I feel like it does, but I’d love to hear what y’all think.