Why have a multi-account AWS environment?
While you can host all your business resources in a single AWS account, this can very quickly become too complex to manage. Imagine hosting multiple resources for your various non-production applications under development, User Acceptance Testing (UAT), and production workloads, all within the same AWS account. This can rapidly become a huge management overhead. The complexity is further compounded because you would have to ensure that many of these applications are isolated from each other for compliance or security reasons. This would require you to define highly complex policies and permissions to ensure proper segregation of different workload types and effective management of resources.
Above all, having a single AWS account prevents you from limiting the blast radius of any major disasters. Separating your workloads using an appropriate strategy will help limit the blast radius of catastrophic disasters. So, for example, you can have...