The default.liquid layout outputs the code for a file upload field on a form as follows:

<div class="row mt-4 file">
  <div class="col">
    <label for="form_field_2_11">Upload Resale Certificate</label>
    <input class="form-control" name="{{ form_builder.fields.properties.form_field_2_11.name }}" data-cfs="3-1-file" type="hidden">
    <input class="form-control" id="form_field_2_11_file" type="file">
  </div>
</div>

I'm building a form wizard with custom JS validation and in slicing and dicing the default form layout  I noticed the "hidden" input field. 

 I've used (and validated) a single <input type="file"> in the past to do file uploads in BC... 

Is there a need or reason to include this hidden input field?  Why is it named and the "file" input field isn't?  What's it do?  What's it's purpose? More to the point, do I need to include this and populate it with javascript??