Role-play
I use them from time to time a crew replacement ship and set them to go from colonies to orbital miners, fuel harvesters and mining sites that only have auto-mines. They represent crew rotation replacement for these installations.
You can also use them as diplomatic ships in multi-faction games and probably many other reasons.
IN VB6 you also could choose to have your characters on specific bodies, then these ships could be used as government ships to house important administrators and transfer them from place to place.