custom curry funtion

curry

const curry = (fn) => {
  if(typeof fn !== 'function') {
    throw Error('No function provided');
  }

  return function curriedFn(...args) {
    if(args.length < fn.length) {
      return function() {
        return curriedFn.apply(null, args.concat([].slice.call(arguments)));
      };
    }
    return fn.apply(null, args);
  };
};

olha esse trecho:
if(args.length < fn.length) { return function() { return curriedFn.apply(null, args.concat([].slice.call(arguments))); }; }
porque nao simplesmente nao é:

`if(args.length < fn.length) {

  return curriedFn.apply(null, args.concat([].slice.call(arguments)));

}`

???