Allows the user to save the currently active workbook as a different name and/or to a different location, leaving the original workbook 'as was'. 

This is a good option when creating versions or when you are not sure if changes you are going to make will work out ('what-if?').  Taking this option has the 'effect' of closing down the original workbook without making any changes since the last save and duplicating it's current state under a new name/location. You can also save workbooks as several different file types via the 'Save as type:' dropdown.  Most useful here are probably the 'text' types, comma-delimited, csv. Tab delimited, txt or space delimited. You can use the space delimited option to produce a fixed width text output by setting the column widths to the width you need. (This may obscure some text but ignore that) and saving as space delimited.

Under the 'Tools>General Options...' menu in this dialog, you have the choice to password protect the file, make automatic back-ups, etc.

It presents the dialog below.