This policy settings controls what is displayed when the user goes to File > Share in Word, Excel, or PowerPoint.
By default, choosing File > Share takes the user to the Share dialog, which provides various choices for sharing. These choices used to appear under File > Share, but no longer appear there by default. There are some additional choices that used to appear under File > Share, but don't appear in the Share dialog.
If you enable this policy setting, the user isn't taken to the Share dialog and the user sees all the sharing choices under File > Share. For example, several options to share by email or an option to share by instant message.
If you disable or don't configure this policy setting, choosing File > Share takes the user to the Share dialog, which doesn't have all the sharing choices.
Note: The user can also add buttons for these additional sharing choices to the ribbon or to the quick access toolbar, regardless of how this policy setting is configured.