Psd files are useful for thousands of reasons. If we find one that looks great, the best idea is to download it, and not because we will use in a project (which depending on your license may well happen), but because being Psd can open it with Photoshop and check our all layers that compose it. The best way to learn how to set up certain effect, a texture or image completely. Whenever I recommend if you are starting to search for and seize these cases.

DesignBlurb published a list of 5 Psd files using textures, to see how they were implemented them and discover that there is no single technique, but depends on the desired project and the experience dequien do.