Byron,
The original Starfleet Command, Empires at War, and Orion Pirates all, if preordered, would have come with Bonus Disks. They generally contained, besides a few bonus missions, some concept artwork for the games, some rather final looking artwork, and that kind of stuff. The reason why most people might have wanted them would have been for the mission scripts, though I guess the modelers might have also been or even more intertested in the design art.