The Save a Copy command does the same thing as the Save command, but with one important difference. It always asks for a file name and saves the image into the XCF file format, but it does not change the name of the active image or mark it as “clean”. As a result, if you try to delete the image, or exit from GIMP, you are informed that the image is “dirty” and given an opportunity to save it.

This command is useful when you want to save a copy of your image in its current state, but continue to work with the original file without interruption.