A common use case is to let the end user select various fragments to insert in the final PDF. The screen shot below would better explain what I mean by this. AS you can see this screen captures some user information, and allows the user to select fragments that need to be inserted in the final pdf. When the user hits the submit button it will call a LC process which will parse the parameters and build the DDX needed for XDP Stitching. The Process makes use of a custom component called xmlUtilities which allows you to insert elements in an xml document. The input parameters to the process are the name,city,address,state,zip and fragments. The fragments variable will hold a comma separated list of selected fragments.
The final stitchedPDF available here and the assets are available as file attachments of the pdf
To get more information on XDP Stitching please visit the following blog by John Brinkman