Once you start having a lot of playbooks and some reusable tasks, you might want to organize them::

playbooks/
  tools/ # Used to manipulate some hosts. Ex: ping, show_groups
  actions/ # For actions. Ex: update, sync, restart, ...
  provisionning/ # Run once provisionning playbooks. Ex: configure ssh, install python, ...
  hosts/ # For playbooks manipulating a single host
  service/ # Content related to a service manipulation. Ex: deploy monitoring on all hosts

.. note: There are various ways to organize playbooks, this is a first draft at how they could be organized