This is one of the many ratios used by auditors in ratio analysis. As with other ratios, the auditor compares the actual value of the ratio at a point of time with the expected value of the ratio.
Any unexpected change is investigated.
To avoid the actual value of the ratio biasing the auditor's estimation of the expected value, auditors estimate the expected value before calculating the actual value. Days to sell inventory provides an estimate of the number of days, on average, that it takes to sell inventory. The value of inventory in the ratio includes the value of work in progress. Average daily cost of sales is equal to total cost of sales divided by 365. By itself, however, the ratio does not convey alot of meaning.