What is the purpose of a 'probationary period' or 'waiting period' for certain conditions in some health policies?

PROBATIONARY/WAITING PERIOD for conditions: A specified period at the START of a policy during which certain conditions or services are NOT covered. HISTORICAL/CERTAIN POLICIES: Used by insurers to manage adverse selection and risk (e.g., a waiting period before maternity or certain conditions are covered); ACA IMPACT: For ACA-compliant MAJOR MEDICAL plans, insurers generally CANNOT impose pre-existing condition exclusions or waiting periods (a key ACA protection); however, some ANCILLARY products (dental, certain supplemental, short-term, or non-ACA plans) may still have waiting periods for specific services; GROUP PLANS: May have an eligibility waiting period before a new employee's coverage begins (e.g., 90 days max under ACA) — different from a condition exclusion; PURPOSE: Prevents people from buying coverage only when they need immediate expensive care; understanding waiting/probationary periods — and that ACA major medical plans largely prohibit pre-existing condition waiting periods while some ancillary products may have service-specific waits — is relevant health insurance exam content.