I'm not into overclocking and never was. It's retarded easy, anymore. I know it is on mine, too. I, personally, never saw the benefits of it since I always ran a quality processor that handled everything I did. Doing it just for bragging rights is pretty damn gay. I'm a firm believer in running an aftermarket heatsink/fan setup instead of OEM, regardless of overclocking.

I can see underclocking on phones and other mobile devices for tweaking battery life.

At the end of the day, do whatever you want. If you can make a mid-range CPU scream without burning it out then I'm all for it. But, I'm content with my 3 year old setup that I can still throw anything at and it doesn't care.