Are you talking about any business scenario? If Yes, Then here could be the scenario :-
1. If you want your transactions to be approved between 2 banks then you must have mandate.
Suppose You have taken a loan from bank A and you want EMI to be deducted from your bank B then in this case you must have a mandate. There will be 3 copies of that mandate 1 is for bank A , 1 is for Bank B and one with you.