Spot also supports hibernate on some instance types: https://aws.amazon.com/about-aws/whats-new/2017/11/amazon-ec... Hibernate is just like good old hibernate from windows XP days. You save the RAM to disk. And resume your processes on next boot and they won't even notice they were stopped! (Except for the time has changed...) It might be really helpful for low priority batch processing. Disclaimer: I've never tested…
This post is different: with on-demand instances you can stop them whenever you like and only be charged for storage while they're in the stopped state and then start them up when you need them again (keeping all the same settings, like the IP, etc). A stop/start is also the way to effectively move your instance to new hardware if there is an instance with the underlying host. Annoyingly, the stop/start API calls were rejected for spot instances. This announcement means this is now finally possible.