The advantage for players playing on the PirateCraft creative server instead of a single player one is that the PirateCraft one would have all the live plugins like MoveCraft at its disposal. This would allow people to test ships before building them live for instance. Mods could help players complete big builds and clear areas for them using WorldEdit.
As Godsy says, really good creations could end up being used in arenas, events, new worlds, etc. If you’re a decent builder, you might be interested in helping to design the PirateCraft hub so people can travel between the servers with little hassle. And if God’s setup proves to be functional, we can expand by adding more servers such as a pirate themed arena server (who doesn’t miss ye olde FFA? 🙁 ).