In GP 2013 R2 there are elements to delegating a workflow. The first is the ability to delegate workflow for a period of time. I’ve covered that type of workflow delegation previously. The second type delegation of an individual transaction an that is controlled via a checkbox in the set up for a particular workflow. Checking the box “allow approver to delegate tasks” lets an approver to delegate individual transactions to someone else for approval. Users get links for Approve, Reject and Delegate.
I really only see this as useful for those scenarios where someone is too busy to really review prior to approving something (In a meeting, boarding a plane, etc.). It might make sense to delegate this at that point to speed up the approval.