The Pencil Trick unlocks the full potential of your CPU. Overclocking the Intel series of CPUs is different than that of an Athlon, and was done mainly by tweaking the FSB of the CPU on the motherboard. FSB overclocking methods, such as running your 300A Celeron set to run at 450MHz by setting the FSB to 100MHz x 4.5 instead of the factory setting of 4.5 x 66MHz, were done very easily. This resulted in a stable overclocked CPU at 450MHz. If you tried overclocking your Athlon in such a way, your system would never POST because the Athlon is not designed like the Intel chip to be compatible at the higher frequencies of an increased FSB. The only drawback to this is that the potential for customers to be ripped of by untrustworthy dealers selling overclocked CPUs to the public at the price of the actual CPU speed is increased by a large margin. Intel long ago locked the multiplier of their CPUs to keep such things from happening with their processors. So with the Intel, chip adjustment of the FSB was the only available option for overclocking.
The Athlon CPU is not designed to handle a high frequency FSB, but will allow you to reconnect the L1 bridges, allowing the processor to be set at any clock frequency, making overclocking an easy task. In the first releases of the Athlon/Duron motherboards you had to not only modify the processor, but you had to modify the motherboard to be able to adjust the Vcore and voltage settings to get a stable overclocked system. But manufacturers soon got the point and started to include those features on their motherboards, making the CPU the only modification you need to make. This works, and is very risk free. The room for error is not great, so even the not-so-mechanically-inclined can take on this task and be successful. I have always been against too much modification, because it can result in the loss of equipment. I wholeheartedly believe in this procedure, as the modification is very minimal and the chance of ruining your equipment is almost zero.