Change default action for copying files to external hard disk The default behaviour on Mac OS when you move files from your machine to an external device is to copy these files. How can I modify this behavior so it moves the files, rather then making copies?
You can move a file rather than copying to another volume (network, external drive, etc.) by simply holding the ⌘ Command key down while dragging the file.

If you are on the samve volume (EG you want to copy to another folder) hold down the ⌥ Option key will dragging and that will copy a file from any location to any other location on the same volume.