The Background Layer:
-is always on the bottom of the stack & cannot be moved (without renaming it to something other than Background Layer)Now, on to why I recommend you NOT work on (or alter) the Background Layer.
-cannot be transparent or contain transparent areas
-cannot be deleted (unless you rename it)
-is locked & cannot be unlocked (unless you rename it)
-cannot have Layer Styles (such as a drop shadow) applied to it
-Blend Mode is always (& only) "Normal"
-Opacity is always (& only) 100%
1) Any editing you do on the Background Layer permanently alters the pixels on the Background Layer. The 'best practice' for processing your image is to work NONDESTRUCTIVELY, which means leaving your Background Layer intact. (More about that later.)**Let's talk about DESTRUCTIVE vs. NONDESTRUCTIVE editing in Photoshop…
2) Think of the Background Layer as your 'original' image file. There are many reason why you might need to go back to the original image and an unaltered Background Layer allows you to do so easily.
3) Layers are at the heart of Photoshop's powerful image-processing capabilities. Layers allow you to make corrections by isolating areas completely from the rest of the image. Once isolated, you can make adjustments and even go back later and fine-tune those adjustments - none of which is possible if you are simply working on the Background Layer!
According to Adobe, "Nondestructive editing allows you to make changes to an image without overwriting the original image data, which remains available in case you want to revert to it. Because nondestructive editing doesn't remove data from an image, the image quality doesn't degrade when you make edits."
When you work on the Background Layer you are using a DESTRUCTIVE editing method!
There are several ways to perform nondestructive editing in Photoshop including:
Adjustment LayersHere's an example of a destructive edit in Photoshop:
Transforming with Smart Objects
Filtering with Smart Filters
Adjusting variations, shadows & highlights with Smart Objects
Retouching on a separate layer
Editing in Camera Raw
Opening Camera Raw files as Smart Objects
Crop using the "Hide" option
Let's say you start with an image of a lush, green rosebush with a red rose in full bloom. You decide to improve the image, drawing attention to the red rose by decreasing the saturation of the green leaves surrounding it.
On the Background Layer (or any other normal layer) you select the green leaves. Using IMAGE > ADJUSTMENTS > HUE/SATURATION you lower the saturation of the selection (the green leaves).
You have just made a permanent change to your image. The saturated green color in the leaves of your original image is now gone forever. You have permanently altered the pixels and you once you save the file you can't get that information back.
[Note: History is not "saved" with the file. Therefore, it cannot be accessed after the file is closed & reopened. Undo is not always available since Photoshop limits the number of steps you can go back, depending on the settings you select in Preferences.]
In this particular case, I would suggest using a Hue/Saturation Adjustment Layer as a NONDESTRUCTIVE edit.
Hope that helps clear things up. If you have any other questions about Photoshop or photography please feel free to email me. The answer to your question may be featured on the blog!