There is a limit to the knowledge which can be obtained about a store's operations without actually visiting the location. Indeed, there are many things you simply cannot learn/notice without being onsite to notice them. Just like a picture is worth a thousand words, a pair of experienced eyes in the field is worth hundreds of phone calls.
Field audits complement financial information (benchmarking) and customer satisfaction results (surveys, kiosks, mystery shoppers) nicely. One cannot paint a complete picture of an individual location without looking at its operations holistically.
Experienced field consultants are often aware of the store's high-level financial information and can easily correlate the audit results with historical financial performance. Their analysis helps them plan adequate business strategies to improve unit-level economics.
The goal of field audits is not to find flaws and reprimand the store manager or employees. Indeed, field audits are standardized evaluations which help a field consultant review all critical aspects of a store's operations. Once the weaker aspects are determined and communicated to the store manager, the consultant works hand-in-hand with the store manager to propose the strategies for resolution. This helps improve accountability but also engages the manager in a constructive manner. Problems are more likely to be solved.
Field audits are a great way to ensure consistency across all locations - as every store aims to respect the same criteria. Without continuous monitoring, each individual location is bound to stray from the established best practices. It is simply human nature to find the easiest way to achieve the same results; but the easiest way is often deceptive. Continuous improvement requires proactive effort and constant course-correcting which are driven, among other things, by field audits.