A (probably silly) question about thread

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When I was at the fabric store recently, I saw huge cones of thread on sale for much cheaper than "normal" thread (spools). Why is this stuff so cheap? Is it only for use on certain things? Also, if I were to buy one of these cones, how the heck would I get it to go in my sewing machine? Just put it off to the side and thread like normal?

Thanks everyone, you all rock.