How to understand the logic of this code and the cluster module?

Question

Node.js

I started to get acquainted with the cluster module, came across an article on Habré . In it, the author shares his code , which, according to him, will balance the loads. I don't understand line 62 in this code:

cluster.on('listening', stopNextWorker);

function stopNextWorker() {
  var i = workersToStop.pop(); //workersToStop - массив воркеров, ожидающих рестарта
  var worker = cluster.workers[i];
  if (worker) stopWorker(worker); //в stopWorker просто выполняется worker.disconnect();
}

Why do we need to kill the worker on the 'listening' event?