Assigning Fields to Signers

Hi, We are brand new to Sign. My question is: When I create a template from an existing PDF, I can manually go through and right click each text field, check box, etc and assign it to a receipient (supervisor, employee or HR manager). This I assume is so during the work flow a person not assigned to those fields can't fill them out.

However, I am also seeing that if I just create the template from an imported PDF and save it without any modifications... then add recipients and 'preview and add form fields', I can drag a selection box around many fields, check boxes, etc and assign those to recipients en masse. Is there a reason for the different assignment locations?

I like the much more efficient way of dragging a box around multiple fields and assigning them to recipients but don't want our HR people to have to do that every time. 

I tried assigning various fields to different recipients while creating the template and it didn't seem to help on the 'preview and add form fields' screen.