Why should an organization have internal auditing?

Internal Audit is a Management Information system.Management by themselves cannot be expected to go through all the records and documents in a company in the available time.So a necessity is there that someone ,internal professional ,has to go through various records and study and report  to information of the Management the deviations and violations from various compliances and also operational efficiency,cost control measures , acting as the eyes and ears of the Management.So Internal Auditing is done.

But Cost control and Budgeting under the Finance controler or Account Manager

To make a control about the organization cost and to know the budget of the year