Gear hobbing

The recent thread about choosing gears for the drive train in a gear hobber left me wondering. You can hob gears by driving the blank with
the hob itself. I just rented a video by Jose Rodriquez that shows how to do it. There are also web sites showing hobbing with hob-driven blanks. This technique seems to work well enough. What makes the independently-driven blank process better enough to justify the highly increased complexity?
Thanks, Bob
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