Sometimes more is less ! Take the time to realize that case and motherboard makers have an idea about airflow. They spent a lot of money doing research in a wind tunnel I am sure. They position things where they do based on there air flow data. Cool air is drawn in the bottom front of the case and it rises. It comes up across the cpu and rises up thru the bottom of the power supply and is exhausted out the rear. The AMD web page show a great diagram of this. aka one picture is worth a thousand words !
When you add a few fans to the sides, in most cases it disrupts the intended airflow. Think about it for a minute. A fan on each side, one in and one out , pulling air across the middle of the case takes air away from the power supply. The air that was going to flow up to the power supply and be drawn across the hot spots of the power supply is now being sucked out the side of the case.
When you change one thing, you may wind up changing things you didn't want to.
Well thats my 2 cents/ Billy