Receivables are the bridge between revenue and cash. If they grow much faster than revenue, the company is either selling to slower payers, extending terms to close deals, or booking sales that will not convert. The measure for this is days-sales-outstanding.
Against them sits the allowance-for-doubtful-accounts, an estimate of what will never be collected. Because it is an estimate, it is one of the easier levers for managing reported profit.
Example: Northwind Tools ends the year with $95M of gross receivables against $840M of revenue, roughly 41 days. A year earlier it was 35 days, so about $14M of cash is tied up by the change alone.
Related: days-sales-outstanding, allowance-for-doubtful-accounts, revenue, working-capital, earnings-quality