Just to play devils advocate without any real knowledge of how this came to be; hypothetical
This may have started out as an experiment to see if there was a better option then one stand alone medium. Maybe the thought was trying to combine two mediums in an attempt to get the benefits from both. Similar to the idea/experiment of breeding an indica with a sativa or two different strains in an attempt to get the best qualities out of both and trying to put them into one plant.
1. From my understanding, plants grow bigger/quicker in straight coco than they do in soil. Maybe the thought was to increase the growth of the plant. While not nearly as much as coco alone, but more than just plain soil.
2. Again, from my understanding, coco needs to be watered multiple times per day due to its inability to retain water and nutrients. Maybe the thought on this was to carry over the water and nutrient retention so it only needs to be watered similarly to soil.
3. With the soil choice of
FFOF, which is known to run hot, maybe cutting/diluting it with coco was an attempt to get the medium from being so hot.
4.
FFOF is often amended with additional perlite due to it's poor drainage. Adding coco may have been an attempt to assist with the drainage. Along with the added perlite.
Some things we do started out as accidents, or an idea someone had, tried, and ended up proving to have some sort of benefit. Other ideas have miserably failed. This probably isn't any different. Someone had an idea and tried it. Is it better? Does it work as intended? I couldn't tell you. It's all I've used so far, so I don't have anything to compare it to. But I do know the person I got this from, who's since stopped running this combination, said while they've ran it this way for a long time, they had difficulty keeping all of the plants happy from start to finish. It always seemed to them like they were dealing with a deficiency at some point or another during their grows. So they've switched back to straight soil.