A comment outcome let's people who completes a checklist leave a written comment. You can have the comment to be optional or required.
To add a comment outcome add an outcome to the template or checklist and select Comment from the outcome options.
Now you will have the option to set the comment to either optional or required.
When a person completes a checklist that has the comment outcome a flyout with the a comment input field will be displayed before the checklist can be completed.