That doesn’t work in all cases. I’ve recently come across two examples where we had a hard time explaining our costs even though we extensively tag and even have fine-grained AWS accounts:
Some costs can’t be tagged or at least not easily, e.g. custom CloudWatch metrics.
For some resources it makes a lot more sense to provide them centrally for multiple services at once, e.g. NAT gateways or load balancers.
That doesn’t work in all cases. I’ve recently come across two examples where we had a hard time explaining our costs even though we extensively tag and even have fine-grained AWS accounts: