Image via WikipediaThese days, you might often copy a video file over to an external drive so that you can take that drive to someone's house. The process can run quite slowly if you drag the video file into the destination drive's window but don't close it. Why is that?
In GNOME, Nautilus is trying to create a preview of the video file every time the file changes ... which is constantly. ;) Nautilus is therefore constantly pulling data from your drive and using CPU to create a thumbnail that will be discarded the next second. Since the bus is probably already saturated with outgoing data, Nautilus is causing all kinds of problems there.
Close the drive's window, and Nautilus won't do that, saving time and energy.