Just scratches the surface. Most guys are adding electrical components that weren't considered when the car was built (stereo, elec. fans, fuel pump etc.).
The added elec. parts requires more power, so adding a higher amp. alternator is necessary. The added amperage over taxes stock electrical stuff so when going to more amp output, you're pushing the limits of the elec. systems ability to deliver power without frying wires.
My 140 amp. powermaster would have left me burnt down on the side of the road long ago if I had used the stock wiring.