Some architectures unintentionally route large volumes of traffic between resources that reside in different Availability Zones—such as database queries, service calls, replication, or logging. While these patterns may be functionally correct, they can lead to unnecessary data transfer charges when the traffic could be contained within a single AZ. Over time, this can become a silent cost driver, especially for chatty microservices, replicated storage layers, or high-throughput pipelines. Re-architecting for AZ-locality—when possible—can reduce these charges without affecting availability in environments where high resilience isn’t required.