Better performance, maximising the capabilities of the hardware, some find it fun and challenging to get a good overclock going.
More heat, reduces the life of the component, voids the warranty, risk of serious damage or death to whatever you're overclocking ANDother components if youdon't know what you're doing, overclocking draws more power.
An overclocked computer is not as risky as it seems. Many people who know what they are doing have successfully overclocked their systems to increase at higher rates, while maintaining stability. Overclocking is recommended to everyone who is wanting extra performance out of their computer