Just as with any computer, a CPU is the heart of your Android smartphone. Install SetCPU and you'll be the equivalent of a digital heart doctor, able to tweak the CPU in myriad ways.
SetCPU is one of the most powerful rooted apps you'll find. Using this app, you can actually control your CPU's settings to maximize its efficiency and speed, depending on your current usage. If you're really busy multitasking and you need maximum possible processing speeds, SetCPU helps you overclock the CPU to squeeze every bit of performance from the chip. Or, when your phone is idle, the app drops the CPU power to conserve battery life.
You don't have to fiddle with SetCPU constantly; just set up profiles for various usage patterns and then click to activate them when necessary.