Patients sometimes can submit treatments costs (e.g., laser treatments) to their insurer in order to receive financial compensation. This is admittedly by the patient themselves because private (aesthetic) healthcare providers usually don't have an agreement with insurers. However, many insurers demand specific declarable codes printed on the invoice. With this feature, it's possible to publish such information with the treatment information on the invoice.
To make your invoices submittable to the insurer, navigate Menu > Record settings > Treatments, select/create the treatment you wish to declare, and fill out the additional information (e.g., an insurance code).