Not just the sets but the camera, too. Whedon wanted the audience to feel like they were in the space, so they wouldn't do the usual tricks of removing walls to set the camera up for stuff like hallway shots. If you watch on the longer shots where they move through the ship you can see the actors turn their shoulders slightly when they pass the camera cause they're squeezing around the corner of the hallway.

That's funny because Serenity never really made sense to me as a ship. Was it supposed to be a cargo ship? The cargo capacity seems pretty low. It also seems to have too many crew members for a ship of that size, and especially to care for that little cargo. It also had an infirmary, which doesn't really make sense on a small cargo ship.

Still, even though the ship didn't really make sense to me as a viable vehicle for a real business, it did make sense as a bunch of connected rooms, so that part they did well.

They did, they built a literal West wing that is still used for shows and ends up larger so cameras can fit and more people can fit side by side.

 A large, fully connected set of the White House allowed the producers to create shots with very few cuts and long, continuous master shots of staff members conversing as they walk through the hallways. 

https://imgur.com/gallery/west-wing-floor-plan-2023-xQcwmpE

^ That person goes very very in depth about the set if you're at all interested.