For their particular situation what would give 8mm film an advantage is that it most likely would have been reversal film. This is a type of film which when developed is already positive, making it immediately useful. Unlike the more common negative film used in still photography and motion picture photography which requires that the original negative image on the film, after processing, needs to then be transferred (duplicated) to another piece of media to create a useful positive image. In the case of still photography the negative image was most commonly duplicated onto photographic paper, the result often being referred to as a "print". In the case of motion pictures the negative image would be duplicated onto another piece of film, creating a film "print", often referred to as an interpositive, which could then be viewed using a film projector or film viewer. This allowed the production team to get an immediate initial impression of shooting results by viewing what was commonly referred to as dailies or rushes.

In the case of reversal motion picture film, which was common in 8mm at the consumer level, and in some cases 16mm at the prosumer or institutional level, the production of "prints" from the original was not required as the processed film was immediately useful for viewing. This was helpful because not all local photo labs were capable of film duplication, which would have been required if the film was shot using negative film. In the 1960's most film processing was done at small local film processing establishments, which were typically only capable of developing film, and in the case of still photography projecting the image onto photographic paper to create prints, as well as multiple prints if requested. Film duplication however was something more specialized.

As a historic example, probably without argument the most famous piece of 8mm film was shot by Abraham Zapruder on November 22nd, 1963 when he inadvertently filmed the assassination of U.S. President John F. Kennedy. Coincidentally this occurred exactly 60 years ago today (this answer was posted on November 22nd, 2023). After meeting with a locally based Secret Service agent, Zapruder agreed to provide the Secret Service with a copy of the film. They went to a local photo lab to have the film processed. Even though the development of the reversal film by the lab produced a useable single copy, the local lab that they went to was not capable of duplicating the film, so they then took the developed film to a commercial film production company in Dallas which was able to make the duplicates.

Reversal film was also popular for still photography, and similar to motion picture reversal film, after being developed the film was immediately usable, and normally placed into a cardboard holder creating what was known as a "slide", which could be viewed in a slide viewer or using a slide projector. However some still photographers preferred reversal film for its particular film qualities even though they planned to use it in the normal methods such as printing onto paper or magazine publishing. However this often created an additional step if the positive image had to be duplicated onto another piece of film to create a negative to be used as a duplication master.

This leads us back to the question of film duplication, which almost always involved multiple intermediate steps, regardless of what type of film was used. As mentioned the camera negative was used to produce an interpositive. This allowed analysis of the color balance and other technical aspects, which could then be corrected when the image was duplicated yet again to another piece of film, known as an internegative. One or more internegatives were then used as masters for creating theatrical prints for distribution. This process could vary, but generally speaking this was the common method.

In the case of the photographers in this film, they apparently saw an advantage in the simplicity of being able to take the completed film to a local neighborhood film lab, or perhaps an acquaintance who had film development equipment, or possibly even developed it themselves, something which was more feasible when using reversal film since no film duplication equipment was required as would be the case if using negative film. And then to avoid the extra steps and perhaps complication of finding a commercial film lab which could produce duplicate copies of their film, they used a clever, or at least unusual method of filming using eight 8mm cameras simultaneously, which after developing gave them the eight copies that they needed.