Right Sizing: Provisioning Instances to Match Workloads
AWS Whitepaper

Conclusion

Right sizing is the most effective way to control cloud costs. It involves continually analyzing instance performance and usage needs and patterns—and then turning off idle instances and right sizing instances that are either overprovisioned or poorly matched to the workload. Because your resource needs are always changing, right sizing must become an ongoing process to continually achieve cost optimization. You can make right sizing a smooth process by establishing a right-sizing schedule for each team, enforcing tagging for all instances, and taking full advantage of the powerful tools that AWS and others provide to simplify resource monitoring and analysis.