I'd also like to add that hot spotting is also usually a "domino effect" type of problem. When a hot spot is formed, that part of the rotor is now thicker. As the rotor rotates, the brake pad will ever so lightly skim the thicker section, thus unevenly heating the rotor with a bias at the hot spot. Of course, you can see why this will lead to very uneven rotor surface after a while of driving.
Also, some awesome info on brakes and related components can be found here on Stoptech's website:
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