PL/SQL User's Guide and Reference
Advantages of Packages
Packages offer several advantages: modularity, easier application design, information hiding, added functionality, and better performance.
Modularity
Packages let you encapsulate logically related types, objects, and subprograms in a named PL/SQL module. Each package is easy to understand, and the interfaces between packages are simple, clear, and well defined. This aids application development.
Easier Application Design
When designing an application, all you need initially is the interface information in the package specifications. You can code and compile a specification without its body. Once the specification has been compiled, stored subprograms that reference the package can be compiled as well. You need not define the package bodies fully until you are ready to complete the application.
Information Hiding
With packages, you can specify which types, objects, and subprograms are public (visible and accessible) or private (hidden and inaccessible). For example, if a package contains four subprograms, three might be public and one private. The package hides the definition of the private subprogram so that only the package (not your application) is affected if the definition changes. This simplifies maintenance and enhancement. Also, by hiding implementation details from users, you protect the integrity of the package.
Added Functionality
Packaged public variables and cursors persist for the duration of a session. So, they can be shared by all subprograms that execute in the environment. Also, they allow you to maintain data across transactions without having to store it in the database.
Better Performance
When you call a packaged subprogram for the first time, the whole package is loaded into memory. Therefore, subsequent calls to related subprograms in the package require no disk I/O.
In addition, packages stop cascading dependencies and so avoid unnecessary recompiling. For example, if you change the definition of a standalone function, Oracle must recompile all stored subprograms that call the function. However, if you change the definition of a packaged function, Oracle need not recompile the calling subprograms because they do not depend on the package body.