even saying that you should have at least 3 USB's man, say you got a gig at a club with 2 CDJ's, say 850's, (or even 900's and 2000's that arent linked via HUD) and you only have 2 usb's and 1 USB Dies which can happen, then your stuck with 1 USB and no way to link the decks, you can pull the USB out of deck 1 to put into deck 2 or it will stop the music on deck 1 thats when backup USB number 3 jumps in