When you need to orchestrate changes across a large number of servers, some of which may not currently be functioning, mcollective is a very good tool. When running Puppet in a large organization there are several tasks that need to be performed in an orchestrated fashion with a small number of machines. In my opinion, Ansible is a great tool for these small changes across multiple machines. I've used Ansible through Git hook scripts to deploy updated code across a set of Puppet master machines. More information on Ansible can be found at http://docs.ansible.com/.