Situation that require a loopback interface in Router OS

Hello for all Mikrotik people there..!
Please anyone can explain in detail when we really need to setup a loopback interface in Mikrotik router.
What is the stuation that require from us to setup a loopback interface in our router and what if we didn’t use it.

Is this some exam question?

WTF,
Why did you start a new thread???
http://forum.mikrotik.com/t/loopback-interface-in-mikrotik/159234/1

It’s not required for regular use. We use it for all our BGP sessions. We use OSPF and redundant links for the backend. If one of the links go down, we can still get to the loopback through the other link.

sometimes on CG-NAT implementation can be useful