Depends on what field you are in... If you are in a field that involves approving blueprints/plans like civil/electrical engineering, then Ir is mandatory for you. And if you are planning to venture into consultancy firms, you also need an Ir..

But for normal manufacturing plants, you don't need an Ir for a manager's position, but an MBA helps a lot. You basic salary might be a bit higher but you'll still start from the bottom as a first level engineer..