The check works by sending a 270 inquiry (patient name, date of birth, member ID) to the payer and receiving a 271 response. The response is standardized but inconsistently filled in: payers populate different service-type codes and benefit fields, and the same benefit can appear under several labels.
For most practices the eligibility check is automated already, inside the EHR or practice management system, and runs on every scheduled appointment. That is worth keeping. What it does not do is apply the procedure code, the rendering provider or the place of service, which is where the patient's actual responsibility is decided.
