What is the difference between “Quick Reject” and “Reject” and “Quick Approve” and “Approve”?

When selecting “Approve” or “Reject,” you'll be taken to a proofing screen of your email. This will let you preview and customize the email before sending it out. 

Selecting “Quick Approve” or “Quick Reject” immediately approves or rejects the request.  It bypasses the email proofing screen and automatically sends the requester the response email.  The response email uses the default email template along with any changes you've made under Setup > Email Content.