What is the difference between needs to view and receives a copy?

The best explanation is the "Needs to View" must open the envelope and confirm, where "Receives a Copy" has no action to perform at all, they just receives a copy of the document based on where the "Receives a Copy" is added into the workflow. Also note that "Needs to View" will get a completed envelope notification (and document attachment) upon envelope completion. "Receives a Copy" does not automatically get a completed notification unless that Recipient Type is added specifically to the end of the workflow.