Each routing policy answers a different "which record" question.
A Private Hosted Zone can span accounts and Regions, centralizing internal DNS.
SimpleOne static answer
WeightedCanary / A-B split
LatencyFastest measured Region
GeolocationCompliance, licensing
FailoverStandby on health-check fail
IP-basedRoute by client IP range
DNS-layer failover (Route 53 health checks) and load-balancer-layer health checks are two separate mechanisms, one hop apart.