When the Mandatory Items setting is enabled, any new items that are added to checklists will be mandatory by default. This is indicated by an asterisk in the top right corner of the checkbox. If you would prefer, you can make specific items optional instead, which will remove the asterisk from the checkbox.
To make a mandatory item optional:
Click on an item in the checklist to open the inline editor.
Click the Make Mandatory button to toggle it off.
If you need to make the item mandatory again in the future, just click the button again to toggle the item back to mandatory.