Non-destructive editing techniques

“Non-destructive editing techniques” describe ways to modify and adjust layers without actually changing the pixel content of the layer. This is a roundabout way to save time in Photoshop – you don’t actually save time on the front end, but you save lots of time and trouble on the back end if you need to go back and make new edits!

Let me give you an example of the difference between “destructive” and non-destructive editing. One common modification for pumping up the contrast on a photo is to use the Image > Levels command and dragging the outer sliders towards the center. This permanently changes the photo (i.e., once you save and close it, there’s no going back), so it’s an example of destructive editing.

Read full article here