Do I need to use the ferrite cores for my Nikon camera?

If I use the Nikon supplies USB cable with my Nikon d3100 do I need to attatch the ferrite cores?

It never hurts.

While the throughput rate might be a bit lower without them, you should still have no problem transferring data due to the CRC checking that is typically done with data transfers.

File transfers just might be a bit slower in an electromagnetically noisy environment without them.

It was nice of Nikon to provide that little bit of extra quality - so why not use them?

Short answer, NO.
The ferrite cores are to reduce electromagnetic radiation from the camera to reduce interference to radios. In practice, they don't do much, but it's enough for the camera manufacturers to meet the stringent requirements on EM radiation as dictated by various government agencies around the world. You do NOT need theses cores unless you find that your camera with the cord is causing your deep space receiver system used to listen for ETs is being compromised. I usually remove these cores, if possible, as they make things cumbersome. They do not affect your data quality at all.