Bag Mockups is a medium or high detailed static representation of the design. Very often mockup is a draft design or even the actual design layout. Mockups are very good for the approval of interested persons, who aren’t involved in the development of a design.
Thanks to the visual nature of mockups, design can be perceived more easily than low-detailed artifacts, and at the same create a rapid prototype. They are good for collecting feedback, and can be used in the documentation.