As for how it works:
The faces are pulled from other management games. The config has been set up to repeat the faces over 1 million times, so you will basically never run out. The pack itself has nearly 15K faces in it, I have used it for a few years and barely seen any repeats in it. It is also a great resource for changing individual faces, as I explain in a video released the 23rd.
This can be needed - because as of yet we haven't figured out how to match the faces with the skin-color/ethnicity coded into the game. I enjoy selecting faces for a few of my regens/newgens every now and again, which is the solution we have right now until the coding bit is finished. It looks like it will take a while to get through though, so I wanted to get this out to you all.