When you adjust a photo using adjustment layers rather than making the alterations to the image layer itself, you can come back at a later time and fine-tune the adjustment. You can also hide the adjustment layer to check how the photo would look if the adjustment were removed, and you can delete it if desired. You can use the Layer Mask thumbnail and clipping paths to vary how much of the image is affected by an adjustment layer.
Use adjustment layers when you need flexibility in your photo editing and where you don’t want to destroy the original image data. When saving the image with its adjustment layers, use a format such as PSD, which saves adjustment layers in the image. This way you can access them whenever you open the image again.