What is the operational audit?

An operational audit is a formal evaluation of the internal systems and procedures a company uses to produce goods or services.
Made of at least four major steps, it tests how efficient and effective production operations are, which ultimately boosts revenue and profits.
It also can reveal ethical issues in the business.
External or internal accountants may perform the review, based on the needs of the business.
This process has some disadvantages, such as potentially high cost, but it also offers advantages, such as new perspectives and increased risk awareness.

Operational auditing in definition is evaluating and reviewing organization's operations in terms of effectiveness and efficiency of the internal system to meet stated objectives.
Normally this process costs high if it has performed by external auditors rather than internal, but in general it's very useful in predicting risks and increasing efficiency of internal system.
Hope this was useful