|Nice place to have citizenship, but you wouldn't wanna live there.|
Number one on my list is the fact that a citizen of one country cannot be conscripted into the military of another. Since the idea of press gangs faded away with the age of sail, military have shied away from using foreign nationals in an attempt to put warm bodies onto ships or into ranks or what ever. This will be especially true in the future of The Black Desert, where grunts and AB Seamen are usually robotic. In fact, one would think that there would be no draft to dodge in my setting, since any military rank under Platoon Sergent is usually filled by something that runs on electricity instead of SOS.
One would think wrong, however. After nearly a half-century of total war on an interplanetary scale, "civilian" in its current usage is an obsolete term. Imagine one parent being actually in the military, the other a "Rosie the Riveter" (even if its the guy) and the kids all in military school. And if you fail out of school, you may be transitioned and spend the rest of eternity as an AI.
If you are a Lunar citizen in a place that actually recognizes that citizenship, then you have many more options. You can't be conscripted, and you can't be Transitioned (One doesn't make criminals into AI; that would be a bad idea). So, in a world of saber-rattling and war-mongering you would be relatively safe. Unless of course, you are thought to be a spy...
Another reason to have citizenship without residency is something I remember from my Army days: Dodging taxes. As a soldier, one technically doesn't have state residency anymore. To put it another way, you can claim residency in any state you like, which is why most of us chose Texas or Virginia. Those two states, in case you didn't know, do not have income tax. We still paid federal taxes (I always wondered why - didn't that mean that our taxes helped pay our own salaries?) but got to keep a few hundred extra at the end of the year. This may be important enough to some people in The Black Desert that they would seek Lunar citizenship, to escape the crushing tithes asked by mega-states of the future. Heck, Charlie Chaplin lived in the US most of his life (until we kicked him out) and never paid a dime of income tax thanks to his British citizenship.
So there you have it, RocketFans: Draft or Taxes, there are a few reasons to be a citizen of one country but not actually live there.