Promises add complexity?

This is the first time ever I read that promises "add complexity over callbacks". Every single other post states the opposite:

javascript复制

fs.readFile('movie.mp4')
  .then(function(data) {
    // do stuff with data
  })
  .error(function(error) {
    // handle error
  })

This adds complexity, and not everyone wants that. Instead of two separate functions node just uses a single callback function. Here are the rules: