The operating system provides some reusable dialog boxes, which provide a user experience consistent with the version of the operating system in which the application is running. The experience also stays consistent across all applications to provide a unique interface for performing common operations such as opening files, saving files, printing files, color selection, and more.
WPF provides these reusable, common dialog boxes as managed wrapper classes, encapsulating the core implementation. This reduces the extra effort creating and managing the common operations.