Midi Interface Question

i recently bought a midi controller/keyboard which came with a usb cable to hook it up to my pc, this seems to work fine for sending midi messages to and fro the pc and keyboard, do i need a midi interface so i can hook it up using its midi ports, is there any advantage in doing so?

if you want to hook it up to your computer via MIDI - ie using it's MIDI ports and not the USB, then yes you will need a USB to MIDI interface. but there's really to reason you would need to do that.

if you wanted to control another hardware synth or sound module with your MIDI keyboard then you would link them together via the MIDI ports and you obviously wouldn't need an interface.

Something devices with USB and MIDI act as a USB->MIDI->USB converter as well. What keyboard do you have?