Do I declare a varable and then return it or just return the result of a calculation and why

Do I do this:

function multiply(num1,num2) {
  let result = num1 * num2;
  return result;
}

Or do I do this:

function multiply(num1,num2) {
  return num1 * num2;
}

And is there a speed difference between them or more memory efficiency?