My players are currently in the process of forming their own organization. Their goal is to build their very own pirate base on an island. But in order to do that, they need labor. Building a base takes time, and of course the players don't want to stop and build stuff. So they hire a work force, and they hire guards to protect that work force. The island they want to build on isn't exactly safe, there are cannibals to worry about. So they need to have enough armed guards to guarantee the safety of the workers on the island.
They are also trying to organize the various pirate factions into one unified fleet. This requires a lot of work, time and diplomacy. This is related to the main premise of the campaign: A foreign fleet is approaching to wipe out all the pirates, so they need as many ships as they can gather, to confront this threat. Basically, their organization is now the driving force behind the many adventures that my players go on.
They have just defeated a rival pirate captain in a glorious sea battle, captured him, and plan to deliver him to an ally of theirs, to gain her military support. And if they succeed, this means more ships that join their fleet, and a powerful ally for their organization.
So yes, I'd say organizations have a purpose. They can drive a campaign.