InDesign works with native Adobe files such as Photoshop, Illustrator, and Acrobat in unique ways. A document may have different requirements for graphics, and InDesign allows you to import different file types, and provides options for controlling how the file is imported. For example, a Photoshop file with layers can be imported as a complete document, or you have the option of importing one (or more) of the layers separately.
In the last exercise, you worked with a Photoshop file with saved paths and alpha channels; however, the file had only a single background layer. When you work with a layered Photoshop file, you can adjust the visibility of the individual layers. Additionally, you can view different layer comps.