What is AWS Certificate Manager Private Certificate Authority, and when would an organization use it instead of public certificates?

ACM Private Certificate Authority lets an organization create its own private certificate authority hierarchy to issue certificates for internal resources, such as internal microservices communicating with each other or internal applications not exposed to the public internet, which is important since public certificate authorities will not issue certificates for internal, non publicly resolvable domain names, and these private certificates can still integrate with ACM for automated deployment and renewal.

aws acm-pca create-certificate-authority --certificate-authority-configuration file://ca-config.json --certificate-authority-type ROOT