Heat and electronics is a bad mixture. Sometimes if the environment in your case gets to hot it can cause malfunctions and freeze your computer. This is bad especially for the overclocker that needs to have a cool case environment to overclock in. Then read on. This is especially important in cooling down a system.
Most people also overlook it when trying to cool off their systems.
What you mainly want to focus on is the air intake and the exhaust. They need to be equal. If you have 5 fans blowing air in and 1 exhausting the air this isn't an efficient setup. It heats up. This is what is happening to your computer when you force more air in than it can exhaust.