However, that final YAML-defined state is not guaranteed to define the entire functionality of the system. The typical counterexample is this: removing a 'create file' clause does not cause that file to be removed on subsequent runs, as the tool has no concept of ownership nor diffing against previous states. The emitted YAML does not represent the indended full state of the machine, just what actions to take to bring it from some unspecified historical state to an underspecified target state. There is no guarantee of consistency.

Thus, it is very easy to get in a situation where an Ansible playbook applied against two machines with slightly different production history will result in very different behaviour.

If you want real declarative configuration management, try Nix/NixOS.