Quick question on array.prototype.concat()

JavaScript
1

I have a question on my code, it’s the one line return I use and the one below. What is the Difference, if any?

var globalArray = [5, 6, 3, 2, 9];
function nonMutatingSort(arr) {
  // Add your code below this line  

  return arr.concat().sort((a, b) => a - b);
  
  // Add your code above this line
}

or using:

return [].concat(arr).sort((a, b) => a - b);

I passed the challenge with the first one, just trying to understand concat() on a deeper level.