What is "Approval Workflow"?

When Any Approver is selected, an email notification will be sent to all approvers, but the leave application requires any one of the approvers to approve in order to make it approved. 

When All Approvers is selected, an email notification will be sent to all approvers, all approvers must approve the leave application in order to make it approved. 

When By Level is selected, the leave application email will be sent to the 1st approver, after the 1st approver is approved, the leave application email will be sent to the 2nd approver and so on. 

The approval level is controlled by the Approver order defined in Employee Master.

Application Status: Pending (No Approver is approved) ⇒ Partially Approved (first Approver is approved) ⇒ Majority Approved (2nd Approver is approved) ⇒ Large Majority Approved (3rd Approver is approved) ⇒ Vast Majority Approved (4th Approver is approved) ⇒ Approved (All Approvers are approved). 

The Approval Workflow for Leave Application is defined at Employee Portal Setup, WebLeave tab

The Approval Workflow for Overtime Compensation Application is defined at Employee Portal Setup, Overtime Compensation Tab

You can also define Approval Workflow in individual Leave Type and Expense Type. So that different Leave Type/Expense Type can have different Approval Workflow settings. 

You can also define Approval Workflow in Employee Master, EPortal tab, which will overwrite the above settings.