The fact that there are so many bolts used to secure the plate tells be it must do something to stiffen the car, otherwise they'd just use a few clips of self tappers.
Even the ribs and folds pressed into the part will when in combination with all those bolts will add to the torsional rigidity of the car, they may even contribute to a reduction in NVH (Noise, Vibration & Harshness)

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