I've made little secret of the fact that I'm a worldbuilding completist, though even I have a limit of what "completist"would actually mean. For example, in my Banshee setting, that meant having a strong sense of what was going on within 30ly of Earth, a solid framework of 100ly from Earth, and a rough sense of 150ly from Earth.
On this level, I've worked out the general concepts behind each nation and culture, and on a map level, the breakdown of districts/provinces and cities. However, for a lot of the areas that aren't Druthal, that's the limit of what I've done.
After all the stories I'm writing, at least right now, take place in Druthal, specifically in the city of Maradaine. Now, I've built Maradaine as a cosmopolitan city, a place where people from all over the nation, as well as the world as a whole, might end up. So it was important to have a sense of the whole country, and how the finer details could affect the city. This was especially true in the case of Way of the Shield, which deals with Maradaine as a capitol city. With Parliament members from Acora, Monim or Linjar, I need a strong sense of what being from those places mean.
Because, after all, who would be interested in reading about that?
*- For my own sense of verisimilitude. In no way will the reading of Thorn or Murder of Mages make you feel like there will be a quiz at the end.