In practice, collective invoices are always used when deliveries to regular customers need to be billed efficiently and cost-effectively for both suppliers, and customers. Here is an example:
Mr. Smith, the master painter, ordered paints, brushes and other materials for his company from the same wholesaler. Instead of paying for each material individually, he settles outstanding invoices on a monthly basis. As a result of this, the wholesaler completes each order with a separate delivery note, and issues Mr. Smith with a collective invoice for all services incurred during the billing period (the last month).
Another area where collective invoices are helpful is long-term supply agreements. For example, the invoice from the electricity provider represents a collective bill over the agreed upon billing period. Physicians and hospitals generally issue collective invoices to health insurance companies, which summarize the individual statements on the health services provided. The same is done for any billing which may fall directly to the patients themselves if their health insurance does not cover a specific procedure.