What is this interior bracket?

['Cuda Hunter]

What is this for?

It is on the passengers side, just above the floor.  Facing forward.

[Bullitt-]

I think that hooks through a grommet that was in the OE carpet...repro carpet does not have
  Mine had something like that on both sides

['Cuda Hunter]

So it is for something that no one uses...? 

[Bullitt-]

I cut a slit in the carpet...it does help keep the corner from slipping I suppose.

['Cuda Hunter]

If you look right in the middle of the slot, you can see where there used to be a bolt or a washer and bolt.
The rust spots in the middle.

Had to hold something.  Was it just for holding the carpet?  Seems ugly for just that. 

[Bullitt-]

I suppose the grommet could rust, it is all covered by the rear interior panel so it's not seen. When installed it is bent over not straight as in your picture.