Those headers would normally go to the front panel USB ports on your case, well some of them anyway. My cases usually only have two front panel USB ports so I use one or two of hose brackets to add a few more ports at the back of my case. My older motherboards only have 4 motherboard mounted USB ports out the back so a having a couple more doesn't hurt. Those brackets are relatively inexpensive anyway. If you hunt a round you should be able to find one with 4 USB ports on it and uses two motherboard headers. That way you only lose the one expansion slot.