With the new settlers its a somewhat random small number, with a potentially sizable bonus if you have a lot of spare food supplies.
I think I'll add something to items so you can see if they're due to be hauled somewhere or not, which should make things a lot clearer.
Yes right now there's no gameplay effect of the lighting, but I'm planning to make it most likely a happiness bonus or malus for working in lit or dark conditions - probably not generally moving about but for any actual work like at a crafting station.