It just means that everything the US petitioner sent to USCIS (original petition and any potential RFEs), the foreign beneficiary should have copies of as well. So the beneficiary knows exactly what documents were sent and what information was put on the forms etc, this helps the beneficiary being prepared for the interview as he/she knows exactly what documents and info the Consular Officer has in front him/her.
Sometimes it can be difficult to remember exact dates for instance, so it's good for the beneficiary to know what dates the petition wrote down on the forms and photos and other documents, so you are both on the same side. The petitioner could also add photos that the CO might ask about at the interview, then it's good that the beneficiary is well aware of the photo and can explain it if needed.
In my case for instance, my then fiance had sent a ridiculous Christmas photo of our stockings on the fireplace, they had both me and my then fiance's names, but also the DOGS names! So the IO was suspicious and asking questions thinking it was our children, and on the forms we had obviously not mentioned any children since we didn't have any. So good to be prepared to answer such questions! 😁