Google Docs Revision History
The Google Doc revision history might be describes as serving two functions. First, should a major problem with the generation of a document occur, the document can be "rolled back" to a previous state. The revision history serves as a flexible backup. Second, the revision history allows the tracking of the development of a document. In educational settings, this might be used to determine when changes were made to a document and if the document was created by multiple authors who did what.
The following video demonstrates these capabilities.