Amazon says

With Auto Scaling, you can automatically replace unhealthy instances to ensure your application remains up and running (learn more about health checks). When new instances are launched or terminated in an Auto Scaling group, you can automate custom tasks, like installing software or retrieving log files, using instance lifecycle hooks.

Also, you can easily attach and detach load balancers from Auto Scaling groups, making fleet management tasks easier. For example, you can perform blue-green deployments, or upgrade SSL certificates more easily and with less downtime. Furthermore, Auto Scaling can automatically apply tags to your EC2 instances so you can see instance cost allocation by tag in your AWS bill. Auto Scaling allows you to see metrics at the Auto Scaling group level, so you can gain insight into the overall performance and health of your fleet.