It's normally used for riser cards on NLX systems. NLX was a ATX based form factor...sort of, that you don't seem much of any more. It was used by OEM's.
You can let that one, and the rest, dangle loosly in the case, I won't tell anyone if you don't tell anyone!
<font color=blue>Watts mean squat if you don't have quality!</font color=blue>