|Excel Developer Reference|
expression A variable that represents an Application object.
When set to True, this property simulates the look of a single-document interface (SDI), which makes it easier to navigate among open workbooks. However, if you work with multiple workbooks while other applications are open, you may want to set this property to False to avoid filling your taskbar with unnecessary buttons.
This example specifies that each open workbook won’t have a separate Windows taskbar button.
|Visual Basic for Applications|