History: What is the role of the duty cycle?

What is the role of the duty cycle?

• The duty cycle is not relevant to simple oscillators.
  The rectangle wave has a duty cycle.
• The duty cycle reduces the amplitudes of the harmonics.
  If by reduces you mean eliminates...
• The duty cycle determines which harmonics to output.
  Yes.
• The duty cycle is how often the oscillator reports.
  I'm not sure what this would mean...