Auto scaling is a fundamental component of compute in the cloud. It provides not only the ability to scale up and down in response to application load, but also redundancy, by ensuring that capacity is always available. Even in the unlikely event of an AZ outage, the auto scaling group will ensure that instances are available to run your application.

Auto scaling also allows you to pay for only the EC2 capacity you need, because underutilized servers can be automatically de-provisioned.