The problem only arises when you have to worry about persistent state. As soon as you have to worry about that, you have to think about backups, replicas, disas

The problem only arises when you have to worry about persistent state. As soon as you have to worry about that, you have to think about backups, replicas, disaster recovery drills and so on. It is much easier to solve for that can of worms for one system than three.