Why is it essential for auditors to do an opening balance test for initial audit engagements?

As the financial data is accumulated in the balance sheet the auditor in case he did not do the previous year audit he/she must confirm the opening balances or refer to the predecessor auditor, or if he/she could not then a disclaimer of an opinion might be necessary in the auditors report, other wise he is carrying out responsibility about the fairness of the financial statements including the opening balances, from previous year, as the auditor is responsible up to the issuance of the audit report.

To verify the progress of the indicators