[Saphire]

Don. the reason I have started using separate layers is, if I make a mistake I can delete the layer and start again, also you can switch the layers on and off so you can see the difference the alterations have made, if you don't like it you can delete the layer without harming the original. I have also been told that if you want to go back to the image at a later time, save it as a psd file and it will keep the layers separate. I have found that if you just do a save into jpg it automatically flattens the layers so you can't go back when you re-open and edit.

Hope I have explained this right.