Against my better judgement, I decided to build my own computer... so I took apart one that I built a couple of years ago and noticed some pins on the mobo that read "chassis fan" and "power fan". They are three pronged pins that stick straight out of the mobo. What are these used for? I know you use a "cpu fan" set for the fan atop the cpu but I don't recall ever using the others. Any help is appreciated!