Use of the control flow statements (return, throw, break and continue) overrides the usage of any control flow statements that might have been used in the try or catch blocks, which is usually not the desired behaviour.

Invalid:

let foo = function () {
  try {
    return 1;
  } catch (err) {
    return 2;
  } finally {
    return 3;
  }
};

let foo = function () {
  try {
    return 1;
  } catch (err) {
    return 2;
  } finally {
    throw new Error();
  }
};

Valid:

let foo = function () {
  try {
    return 1;
  } catch (err) {
    return 2;
  } finally {
    console.log("hola!");
  }
};