By duplicating the Background layer you save a kind of a backup copy of your original image. Also, it enables you to correct the effect of sharpening, retouching, painting, etc. even after you re-open the image.
Note that in Photoshop 7, in case you duplicate the Background layer
by using [Ctrl+J] shortcut (command Layer Via Copy), the copied
layer inherits the locked position property (animation).
For more details on layers read the Skills chapter.

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