The only video hints at it, but what is something that can be manufactured in space in their station that can't be manufactured on earth?
The ISS was built after lots of launches of components, they can also build small satellites or other things that stay in space.
That's the current use. But in the far future, space ships or habitats probably. Things that can't hold together under the weight of gravity or areodynamic drag. Like tyco station in the expanse.