Understanding Papaparse

Question

I am trying to understand Papaparse. I see a lot of examples do something like this

var file = evt.target.files[0];

Papa.parse(file, {
    header: true,
    dynamicTyping: true,
    complete: function(results) {
    data = results;
  }
});

This is nice and simple, directly parse a file.

However, at the same time I see some examples like so

upload (e) {
    const that = this
    const fileToLoad = event.target.files[0]
    const reader = new FileReader()
    reader.onload = fileLoadedEvent => {
      Papa.parse(fileLoadedEvent.target.result, {
        header: true,
        complete (results) {
          console.log('complete', results)
          that.doc = JSON.stringify(results.data, null, 2)
        },
        error (errors) {
          console.log('error', errors)
        }
      })
    }
    reader.readAsText(fileToLoad)
  },

That is a vuejs function, but I see other examples like this. So why do some call Papaparse directly, whilst others use a Filereader to load the file before parsing?

Just trying to understand the difference between the two approaches?

Thanks

Example using Webworker and Filereader HERE Example doing a direct parse HERE