Shared mode in Excel 2007, 2010 and 2013 tracks every change made to a workbook and allows up to 256 users on a network to collaborate simultaneously. Without shared mode, any users who access a file after the first user can open it just in read-only mode. However, sharing a workbook severely limits Excel's available features, so turn it off from the Review tab to recover functionality when you're the only person using a file.
Turn Shared Mode On or Off
To toggle shared mode, click "Share Workbook" and check or uncheck the "Allow Changes..." box on the Editing tab. Alternatively, remove a specific user from a shared workbook by selecting a user on the Editing tab and pressing "Remove User." Disabling shared mode causes several immediate changes to a workbook, so before turning it off, check the effects to make sure you're ready to shut down sharing.
Effects of Disabling Shared Mode
As soon as you turn off sharing, all other users lose the ability to save changes, even if they're still actively working in a file. Disabling sharing also erases the change history, which keeps a record of every modification. To keep this history, press "Track Changes" on the Review tab and pick "Highlight Changes." Set the "When" option to "All," and check "List Changes on a New Sheet." Open the new History sheet, select the entire list of changes, copy it by pressing "Ctrl-C," start a new workbook and paste the list by pressing "Ctrl-V." As an alternative, save a second copy of your workbook and turn off sharing in only one version. This method ensures that you retain both the list of changes and a copy of the book where the contents match those changes.
Disadvantages of Shared Mode
Despite shared mode's benefits, enabling the feature prevents you, and all other users, from accessing several basic features in Excel. For example, you can't merge or split cells, create tables, delete worksheets or insert objects such as pictures. Excel grays out unavailable options while in shared mode, including nearly the entire Insert tab. By turning off shared mode, you regain access to all of these features. As a workaround if you need these features but have multiple contributors, you can still edit a workbook on multiple computers even without shared mode -- just not simultaneously.
Move Back and Forth
If you need both shared mode and the features disabled by shared mode, but aren't concerned about tracking the change history, switch sharing on and off as needed. Most of the features disabled by shared mode work fine as long as they exist in the file prior to sharing -- you just can't change them with it enabled. For example, to add an image, turn off sharing, insert the picture and re-enable sharing. One major limitation: you can't share a workbook containing a table. To remove a table without losing data, right-click the table, choose "Table" and click "Convert to Range."