A common pattern in several companies using AWS services is having several distinct AWS accounts, partitioned not only by teams, but also by environments, such as develop, staging, production.
This can very easily explode your budget with not utilized resources. A classic example occurs when automated pipelines – think of terraform apply, or CI/CD procedures, etc – fail or time out, and all the resources created in the meanwhile are left behind.
Another frequent example happens in companies recently moving to the cloud. They create accounts for the sole purpose of familiarizing and educating developers on AWS and doing quick and dirty experiments. Understandably, after clicking around and creating multiple resources, it becomes hard to track exactly what was instantiated, and so unused zombie resources are left lingering around.