There are also terrain models, which actually work pretty well. It's pretty much the only use for such enormous models. They're a priceless resource for any mod that wants to include flying in atmosphere, but there isn't many of them, and most are lo-poly. In general, any big object, be that terrain or a very large space station, is most useful as a "mission environment". There's an enormous mission design potential in there, but due to the difficulty of making both assets and missions using them (AI crashing tendencies don't help), it's barely touched in most existing campaigns.