This policy setting controls whether Excel can exchange data with other applications that use Dynamic Data Exchange (DDE).
If you enable this policy setting, Excel does not allow the exchange of data with other applications that use DDE. In addition, the "Ignore other applications that use Dynamic Data Exchange (DDE)" user interface option under Excel Options | General is selected and users cannot change it. Enabling this policy setting can cause disruptions for users who rely on the DDE functionality in Excel to update information in workbooks. These users will have to use some other method to update information provided by other applications.
If you disable or do not configure this policy setting, Excel can use the Dynamic Data Exchange (DDE) protocol to exchange messages and data with other applications. For example, a cell in an Excel workbook can be dynamically linked to a value provided by another application, such as weather or stock price information. When the value provided by the other application changes, Excel can automatically update the value in the workbook. Note: users can change this behavior by selecting the "Ignore other applications that use Dynamic Data Exchange (DDE)" user interface option under Excel Options | General.