it's the sill plate extension. it interlocks with the long sill plate, both of which go over the carpet. they are also side-specific. i don't have a picture of it interlocking, but this one has the arrow to show where it goes:
With a little help from my friends😁Before sill plate and carpet I believe I don’t think it has anything to do with carpet install. Like Southbay said just there to protect the wires and maybe the bottom of the seat from the pinch weld?
U gonna get that thing done this year? 😎