Decline & Send back gives approvers the ability to decline an Approval without stopping the existing Approval request allowing the user to reroute to the previous step or multiple users in the approval.  Each approval group setup can be configured as needed as this is not a global setting. 

To manage approval settings begin here:  Toolbar> Approval  Groups > Edit Details per Approval Group to configure the best option: 

Option #1: Send Back to selected Approval step(s)

The first option displayed below allows the approver to decline the approval and send it back to one specific approver or multiple approvers in order to keep the approval request flowing. 

Option #2: Send Back to an approval step in the Approval:

In the image displayed below, an approver can decline once the  and send it back to the previous step to be actioned. 

Related Articles:

1. Administrator - Creating Approval Groups