Once you have launched Amazon EC2 instances, you get the ability to save your root device data on the local instance store or Amazon EBS. When you use Amazon EBS, the data on the core tool persists autonomously the moment the instance starts. This makes it easier for you to stop or restart the tool when you need to do that. This is important and we can compare it to when you need to start or shut down your computer.
Likewise, the persistence of the local instance store is only during the lifetime of the instance. This is a cheap way to launch instances where information is not stored in the root device. For instance, some individuals use this option to operate massive websites, whereby each instance is able to handle web traffic. This enables them to operate the websites cheaply and more efficiently than they could otherwise have done.