what
Accept external S3 bucket
why
The bucket could be from the same ASW account or from a different account.
This is useful if an organization uses a number of separate AWS accounts to isolate the Audit environment from other environments (production, staging, development).
In this case, you create CloudTrail in the production environment (production AWS account),
while the S3 bucket to store the CloudTrail logs is created in the Audit AWS account, restricting access to the logs only to the users/groups from the Audit account.