I had a requirement at my work for designing a Document Management using SharePoint 2013 and here is my proposed design.
Document Center site is designed to managed an enterprise's live documents. Users can perform different functions like create, upload, edit, check-out/in, document set, search etc on a document.
Records Center site is designed to retain the expired/retired documents which are no longer required in a project but an enterprise keeps them for the record.
The whole life cycle would be, user will create the document on his machine and then upload it to the Document Center where a unique DocumentID will be assigned to it. The document will be live at that point, meaning it will be available for edit, check-out/check-in, search etc in the Document Center. When its time to retire the document, it will be sent to Record Center where it will be available as a Read-Only Document.