Budget season

All, with budgets being prepared by management I woud like to learn more how you typically approach such discussions. For instance, how do you assess if the right level of ambition is set? in terms of Opex, to what extent is zero-based budgetting customary? 

Of course I understand that these discussions depend on many things including the performance of the PortCo and the size/complexity of the business - anyways happy to learn more!