(Unknown Title)

I think you only need that 4pin molex on the mobo with certain CPU's or if heavily OC'in the CPU itself Cool

Edit:Ooppps,its an extra SLI / XFIRE Power Connector Shocked

I would always use it, as it will not hinder anything by it being plugged in. But yes it is to provide supplemental power to the mobo's pci-e power.