Overclocking is an easy way of getting more performance with small means. This can result in a more pleasant gaming experience, or save time when rendering models. The drawbacks of overclocking are fairly few if done right, but there is no way to get around the fact that the power consumption increases. Something that both raise costs and could result in cooling problems. At X-bit Labs they have shared an exciting article that goes in depth.
It has tested overclocking no less than nine popular processors from and AMD and Intel. The intent was to see how both performance and power consumption scaled with overclocking.
They tried to overclock by only raising the clock frequency, but also by increasing the voltage. You have to be blind not to see the obvious here, voltage is the biggest culprit of them all.
A Core i7 950 processor increase the power consumption with nearly 127W with an increase in voltage and frequency (1.2V stock to 1,4V at 4,2GHz).
The articles offers a lot of value on how overclocking can boost performance, but also what you lose in higher power consumption and heat production.