The Ansible debugger is an extremely useful option to enable when you are working on creating large playbooks—for example, imagine that you have a playbook that takes about 20 minutes to run, but there is an error somewhere toward the end, say, 15 minutes after you first run the playbook.
Having Ansible drop into the interactive debugger shell not only means you can see exactly what is and isn't defined, but it also means that you don't have to blindly make changes to your playbook and then wait another 15 minutes to see whether those changes resolved whatever was causing the fatal error.
