We often use document set to group similar documents.

The idea, I when we place a document set into a location, and we set the document set to the proper state, all the access to his location will be add to the access rights of the document.

If no workflow, the folder access will be add to the documents.

This will allow us to get more flexibility in sharing document without having to duplicate or move them around.

The same logic could be apply to custom folders. We create a custom folder and set the access that would be add to the existing one.