We have a SharePoint site within our department where people outside the department do not have access. However due to the nature of our work, we require responses to our work from people outside the department. Do they need site access to be able to view and approve (with comments) the workflow item????
If you want to know who they are then you would need to track that in some way. If you wanted to use anonymous forms, you could achieve that but require that they input their name and email address as a soft capture of who they are, but this is not as guaranteed as having credentials.
Just depends on your requirements and what you needed out of it.