At least in the context of, "there is something that every single person needs to know about immediately." If the nukes are coming down, I'd prefer not to know honestly. Localized alerts make sense, weather do be like that, and I suppose the point of a "nation wide system" is for everyone to be on the same (, universally supported) system and it can be used for local alerts.
Otherwise localized alerts are just used for whatever the po po what to blast out and they can piss off.