Most of the time cases have side openings so you can funnel colder outside air to the Processor(air blowing in) to cool it slightly more than normal. Processor fans blow down onto the heatsink to not only cool the CPU but also to cool the capacitors and chipsets around the CPU socket. Some people even add an additional fan to the side cover in front of the usual funnel to the cpu hoping to increase the cooling but i think this is overkill because when i tryed it the result was only 1° C difference. I've had much better luck cutting a hole in the top of the case and installing a fan there. Temp difference was 4° C(15° F). This does not work on cases specifically designed for good cooling. I'm cheap, so a little time and a $5 fan on a cheap $30 case is cheaper than a $125 case.