You can arrange independent pages to create ganged layouts that make effective use of the press runs.
Mixed-size, flat-work products can be ganged on the same press run:
 

You can step-and-repeat a page to fill a selected area on the press sheet with duplicates, which is useful for jobs such as business cards.
 

For nested work, you overlap pages, typically for press sheets that are being finished with die-cutting. The input files require transparent backgrounds.
 
 

You can completely overlay independent pages, resulting in what is traditionally called a double burn. The final imposed page combines two or more images, depending on how many pages you overlay.

This technique is useful for products that use the same content on each page plus additional or changing information. 

Depending on the intended use, the input files of the overlaying pages might require transparent backgrounds.