What's the difference between NgcLoader and awesome-typescript-loader?

Question

I'm reading this article about @ngtools/webpack NgcLoader and it has the following code:

if (envOptions.MODE === 'prod') {
  config.module.rules.push(
    { test: /\.ts$/, loaders: ['@ngtools/webpack'] }
  );
  ...
} else {
  config.module.rules.push(
    { test: /\.ts$/, loaders: ['awesome-typescript-loader', 'angular2-template-loader'] }
  );
}

I'm wondering what's the difference between NgcLoader and awesome-typescript-loader. Why not use NgcLoader exclusively?