Stable voltages and undistorted waveforms are two characteristics which are very desirable in power systems. Grounding affects voltage stability, and more importantly, is critical to personal safety. Harmonics are a mathematical model we use to analyze distorted waveforms.
Harmonics are a mathematical model of the real world.
Let's examine how these power supplies operate. There is a law in electrical engineering called Ohm's Law. This basic law states that when a voltage is applied across a resistance, current will flow. This is how all electrical equipment operates. The utilities do a wonderful job of generating this voltage sinewave.