is upload position or order matters?

[codenoobforreal]

After I read through the doc I found out there are two way to write the handler function

app.post('/profile', function (req, res) {
  upload(req, res, function (err) {
    if (err instanceof multer.MulterError) {
      // A Multer error occurred when uploading.
    } else if (err) {
      // An unknown error occurred when uploading.
    }

    // Everything went fine.
  })
})

app.post('/profile', upload.single('avatar'), function (req, res, next) {
  // req.file is the `avatar` file
  // req.body will hold the text fields, if there were any
})

the second one the upload comes first.
what is the difference?
which one do I choose?