This is something that I ran across in Charleston a few years ago. The reasoning behind it was that if the soil got washed away in a hurricane or tropical storm then the feeders of the duct bank would not get as easily destroyed and washed away. We installed these on all of the duct banks on a huge multi-use facility. We just made sure to use a transom to determine where the slab was going to be so that the tops of the rods in the rod holders were in approximately in the center of the slab. They were still a pain to install and reminded me a little of the seismic supports needed in earthquake prone areas