History: Why do we use equalizers?

Why do we use equalizers?

• To make a single sound source clearer.
  You can use it for that, but that isn't the main purpose...
• To make multiple sound sources combine together clearly by avoiding overlapping frequency ranges.
  Excellent!
• To make multiple sound sources fight each other by adding overlapping frequency ranges.
  That could be artistic, but not the typical use case...
• To have the instruments hold a fair democratic election.
  Nope.