Advice on an efficient sharing strategy
In the long run, it is better to share folders rather than documents, because any item added to a shared folder automatically inherits access permissions from those of the folder. In addition, explicitly sharing documents with collaborators adds them to their Shared with Me unstructured collection of shared items, and may thus render them difficult to find; in practice, this will force your collaborators to move such documents in the right place, a folder; so why not do it yourself in the first place?
This is why we show how to share for folders only, although the interface is basically the same for sharing folders or documents.
A good strategy is to share big folders with collaborators, and never use explicit sharing for documents: just upload the documents to be shared in the shared folder, and they will automatically be shared by the right persons. Rely on a good organization of your folders for efficient sharing.
For an efficient collaboration, trust your collaborators: grant them edit permission, and the permission to add collaborators as well. Trusted collaborators can make mistakes, but mistakes are usually not a serious problem, because Google maintains document versions, so that you can easily go back to a previous version of a document. As far as the folder organization is concerned, in case of a serious mistake, you can usually fix it, for instance, by retrieving some folder that would have been misplaced, or even thrown into someone's Trash can. On the average, very little time is spent fixing such mistakes, compared to the benefits of a non paranoid attitude.