Lower grate Question

I just used Herb's method of reverse searing a ribeye. Best damn steak I've had in a long time. Wife raved over them and she's one of those that doesn't particularly like to eat red meat. Said she'd eat steaks all the time if they always tasted like this.
I do have a question regarding the process. The instructions said to remove the lower grates and put GrillGrates on the chimney side until searing time. Is there a reason the lower grates would have to be removed? Could they be left in and just stacked to one side?

I do have a question regarding the process. The instructions said to remove the lower grates and put GrillGrates on the chimney side until searing time. Is there a reason the lower grates would have to be removed? Could they be left in and just stacked to one side?