As you can see, with Current Layer selected, the clone stamp ignores pixel
data contained in any other layer. Conversely, All Layers ignores all layer
distinction and clones any visible pixels in the document (invisible layers
will be ignored). Finally, Current & Below samples pixels from the selected
layer and any visible layers behind it.
Basic Settings: Adjustment Layers
The final basic setting (the circle with a diagonal line through it) lets you
decide whether the clone stamp tool should sample adjustment layers
when cloning. Adjustment layers, such as Hue/Saturation and Levels, are
meant to be a non-destructive way to change the appearance of layers. So,
you can make drastic changes to a layer or group of layers without
destroying the original pixels.
Because of this, turning on Ignore Adjustment Layers When Cloning is
almost always a good idea. This allows you to clone the original image,
which can then be affected by an ever-changeable adjustment layer. If you
do not choose to ignore the adjustment layer, the adjustment becomes
permanent in the cloned areas.
In the layer set-up below, turning on Sample All Layers would by default
clone pixels from both the background layer and the adjustment layer in
the foreground. Turning on Ignore Adjustment Layers prevents this.