Repeating pages are just that, pages that repeat multiple times in the same project.
For example, when working on a large hotel, the architect may provide an image file called "Floors 2 - 5" - all the floors are exactly the same. Use Repeating Pages on the cover sheet to indicate that this image file repeats 4 times. Then takeoff the objects ONCE and the takeoff would be repeated on each virtual page.
See Typical Pages for more information regarding this feature.