Grouping classes into applications enables you to work easily with only the classes for a particular application. Imagine what it would be like to use a file system without folders or directories. Computer users would have to deal with one long list of files, which is an almost unmanageable problem for a system that has more than a few files. The same is true of classes in an image. Grouping classes by application significantly reduces the complexity of working on a set of classes. Further, placing classes into applications and controlling the set of applications that a program uses identifies the classes that are needed and those that are not needed.