They are for the silly ASUS PIKE slot at the end of the board - this seems to be a good deal for a LSI SAS 2008 chipset and probably avoids the counterfeits that plague the used market as this is an obscure part.
LSI SAS 2008 Features: IT Mode. SR-IOV with ARI (if coreboot ever supports it) 16 VF functions. FLR (function level reset) for pain free IOMMU VM assignment Works without Option ROM loading
Notes: I thought the SAS 2308 was the first with SR-IOV but this one apparently has it too according to LSPCI, I have never used SR-IOV with a HBA/RAID card but the idea seems to be that you can assign RAID arrays or individual drives to a VF then assign the VF to a VM.
You screw in one end of the massive heatsink via the motherboard screw in that location and the other end clips on to the PCI-e slot (make sure it properly clips and is properly seated, I had a difficult time with this and had to remove and re-attach one of the clip screws to get it to seat)
I advise re-flashing this in a VM on a PC without option ROM support, as all the sellers are chinese. Offical firmware (hard to find this link) https://docs.broadcom.com/docs/9211_8i_Package_P20_IR_IT_FW_BIOS_for_MSDOS_W...
Unfortunately they have proprietary firmware like all SAS cards but at least as they are used you aren't supporting further non-free development.