What would the difference be between an Excel spreadsheet sitting on an external hard drive being used as a backup copy, and that same Excel spreadsheet being e

What would the difference be between an Excel spreadsheet sitting on an external hard drive being used as a backup copy, and that same Excel spreadsheet being emailed to an acquaintance or customer for a work purpose? Locking everyone out based on the Microsoft Account of the creator would break so many things in the Office ecosystem, I can't fathom that being worth trying to implement.