Prior to running these, i'm doing an ssh-copy-id of my key to all nodes, to speed up the process.
Mainly I'm using these for one-off execution of logic, using:
ansible-playbook -i inventory -K playbook.yml
The .retry files are leftovers from ansible runs, and can be ignored (but will be regenerated when things fail)
And for the lazy, who don't want to keep typing their sudo password:
ansible-playbook -i inventory --extra-vars 'ansible_become_pass=blah' playbook.yml