If you have a big binary file (many megabytes), and require it at various places in your SVN tree (branches or patches for exemple), the client will download the very same file for each copy. On a LAN this is not a problem, but when you use SVN over the Internet (or any slow connection), it can take hours to update a local-copy. SVN should be able to say something like this: "Add this file, but I already sent it to you. Copy the previous file to this new location and apply the following delta..."
Original issue reported by ozonegrif