Req approval Actions-- Reassign functionality (Reassign Vs delegate) and Adhoc Route options

Content

Need to understand what is the difference in the Req approval notifications - Reassign functionality. I see there are two options when the approver selects Reassign option 

• Reassign (Transfer task to another user or Group)
• Delegate ( Allow specified user to act on my behalf)

Also there is an another option - Adhoc Route in the approval actions. Need to understand the behaviour between the Reassign options and the adhoc route options. How the approval works when the approvers selects between the 3 options. Also what is the approval hierarchy that is generated when the approver selects between two reassign options and Adhoc route Options.