The best reason to run Night's Watch, and just about the only reason to run Night's Watch Fealty. These birds get you good card draw very cheaply, and can double as claim soak if you need it.
They also have different weaknesses than most factions card draw, since they're not a location. And they are generally safe from Wildfire Assault if you play one at a time.
They can be a bit of a liability against Targaryen, since Plaza of Punishment can easily take them out.