AWS organizations allow you to consolidate multiple AWS accounts into an organization that
you create and centrally manage. Unused reserved instances (RIs) for EC2 are applied across
the group so the organization can utilize their unused reserved instance instead of
consuming on-demand instances which will lower their costs
You cannot redeem your reserved instances. You can sell them on the AWS marketplace however
Using placement groups will not lower their costs
Spot instance pricing is variable so it is not guaranteed to lower the cost and it is not
suitable for workloads that cannot be unexpectedly terminated by AWS