What is this express middleware preventing of?

JavaScript
1

In the mongoose exercises, the last middleware is:

// Unmatched routes handler
app.use(function (req, res) {
  if (req.method.toLowerCase() === "options") {
    res.end();
  } else {
    res.status(404).type("txt").send("Not Found");
  }
});

this will only be executed when a request does not match neither the previous routes+methods. Now, why not writing this:

// Unmatched routes handler
app.use(function (req, res) {
      res.status(404).type("txt").send("Not Found");
  });

Surely I’m missing something, so that’s why I’d like some ideas!!