History: Why do we use low frequency oscillators?

Why do we use low frequency oscillators?

• There is no purpose.
  Nihilism isn't cute.
• The purpose is to set static parameters.
  The opposite is true.
• The purpose is to make our music smarter.
  While LFOs add interest, there's something more basic going on.
• The purpose is to change a parameter over time.
  Correct!