As a general rule, I have seen 'reject' used instead of 'request change'. There are two differences:
1) Request changes has you select the user (assumes you know who submitted or who was in the workflow before it go to you) but reject automatically sends it back to submitter.
2) Reject starts a new workflow and the request change continues with the same workflow. Workflow history is maintained for both, but it's a matter of viewing it differently.
TechNet says that you should be able to use either, but we have seen issues with editing the appropriate fields using the 'request change' functionality and most people don't like having to select the user.
------------------------------
Shirley Adams
AKA Enterprise Solutions
New York NY
------------------------------
Original Message:
Sent: 08-03-2017 18:01
From: Elsa Yang-Brown
Subject: Workflow - Request change functionality
Hello -
We are currently using Dynamics 365 with Axtension Invoice processing and I have a few questions regarding the "request change" option in Invoice workflow. We are trying to use the request change button to route an invoice back to the person who coded it but we are getting the error message shown below:

Does this message look familiar? We are having trouble figuring out what type of access is missing that is preventing the original invoice coder from getting the invoice back. Does the "request change" option allow you to send the invoice to anyone? Or is there something in the workflow that is only allowing certain users the ability to receive the invoice? Right now, it looks like we are only able to assign invoices under "request change" to our 2 AP roles.
Any information would be very much appreciated!
------------------------------
Elsa Yang-Brown
Sempra US Gas & Power
San Diego CA
------------------------------