Multiple AWS accounts is definitely a best practice in larger engineering orgs. We implemented a CloudFormation StackSet to ingest them into our billing tool and lay them out appropriately. This proved to be a very slick solution from AWS so it made me believe that they want their larger customers to use multiple accounts too.

If you are smaller I would not recommend it. Many things become a little more difficult, as others have pointed out. Oftentimes a devops or platform engineering org will paper over these things.