Ad hoc commands allow you to quickly create and execute one-off commands, without keeping any record of what was done (other than perhaps your shell history). These serve an important purpose and can be very valuable in getting small changes made quickly and for learning Ansible and its modules.
Playbooks, by contrast, are logically organized sets of tasks (each could conceivably be an ad hoc command), put together in a sequence that performs one bigger action. The addition of conditional logic, error handling, and so on means that, very often, the benefits of playbooks outweigh the usefulness of ad hoc commands. In addition, provided you keep them organized, you will have copies of all previous playbooks ...
