What are the different advantages and disadvantages of internal audit?

Advantages of Internal Audit are following:
It is in-expensive.
No charted accounted is required to audit internally.
Errors will be removed before preparing financial statements.
There will not be any type of embarrassment in the society because errors have been removed.
Accounting staff will remain in pressure so record will remain update every time in the organization.
Disadvantages are following:
Internal audit is not acceptable by the shareholder.
There can be errors in internal audit because he is not an auditor.
And there are some more.