This could be important in determining the timeline of events; to see if the physical state of the drives match up with the data on the machines. Hard drives degrade over time naturally. They lose their charge or otherwise break down over time. I'm thinking if you looked really closely (like down to the molecular level) you could tell if the data was written on election night or if it was written over with falsified data.

You can not do this with an image copy of the original drives.