How do power consumption and size-of-smallest-feature matter when buying a processor?

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http://serverfault.com – Background: I am shopping for processors to build a server on Newegg. The first bullet point on each processor displays the size of the chip in nm and its wattage. Why? I am looking at the number of cores, clock speed, cache, socket type (for mb), branch predictor (& assoc. architecture), etc. Question: What is the substance in showing the size of the chip and wattage? What should I focus on with these values? (HowTos)