Tax audit affects revenue collection in that it promotes voluntary compliance of taxpayers which increases revenue. It also determines the accuracy of returns so as to ensure the right taxes are submitted. With tax audit tax liability can be easily declared and matters that need adjustment are identified.
In my opinion I think this question is more about the "reliability of Tax Audit in revenue collection" than just the process itself... In the Accountancy profession It is very important to understand the language... For the fact that the question is based on Tax Audit (not Tax review) the opinion that the Auditor will Express will give a "reasonable assurance" that the Income Tax as calculated by the client or taxpayer is free from all material misstatements either due to fraud or error... it is very important to note that this Assurance is "not Absolute"... Tax Audit does help the Commissioner of Inland Revenue to collect revenues from taxpayers and that is without a doubt.