The feature of "delegation" of approvals is not robust. It is fully reliant of users remember to set the delegation prior to leaving, which rarely happens. (We are lucky to just get their email out of office set... Workfront is rarely remembered).
Additionally, it does not cover sick days or other unexpected out of offices.
Feature request: Create a function to declare a permanent backup approver, who can act on behalf of the main approver. It would be best to be able to declare a user, variable settings like "approver's manager" or "program owner", etc.
Current work-around: We are currently adding a 2nd or 3rd person to every approval, with an informal agreement that one person should be considered the primary, and the others only act on an "as-needed" basis. This works, but creates confusion around who truly owns the approval responsibility.