Some cases the file format is determined by the client and circumstances. For example, a level 10 JPEG 300DPI broken into three parts Front,Back, Spine, may be required for a cover when you don't have a FTP site. If the client requires a 300DPI, PSD Flat of the entire cover, the file may run 40megs, (or more), and cannot be E-Mailed. In that case you either put the image on a disk, or get a FTP site. PSD-High quality-layers option TIFF- High Quailty Image- but no layers option JPEG-Good image at highter levels of quality