According to the CIS AWS (Center for Internet Security AWS) benchmarks, unauthorized API calls should be closely monitored because they indicate potential security threats or malicious activity within the AWS environment. Monitoring unauthorized API calls helps detect unauthorized access, misconfigurations, or attempts to exploit cloud resources. It's a key part of maintaining a secure AWS environment and helps ensure compliance with security best practices.

Regular file backups are important but not specifically a focus of the CIS AWS benchmarks. Data encryption at rest is a security best practice but monitoring unauthorized API calls directly addresses access control and security within the environment. Successful login attempts are important but monitoring failed login attempts (as opposed to successful ones) is generally a better practice for identifying suspicious activity.