A checklist item that is marked as optional* at the template level will display with an “Optional” label next to the item on the status page:
Manually Added Checklist Items
If a checklist requirement is added manually to an applicant's checklist via the "Insert Requirement" link via the application tab of a person record and that checklist item is marked as optional, this will not override the optional setting set at the template level (i.e. it will not list as optional on an applicant's checklist if the template is set to required).
Manually Added Optional Custom Item
For truly optional manually added checklist items, a best practice would be to select 'Custom' for the Section setting, and then add the name of the requirement manually in the Summary field.
A checklist item can also be marked as 'Optional for reading.'
Regardless of whether the checklist template is marked as required or not, designating an item as 'Optional for reading' will make it so that the absence of this item from a person's record will not hold up the reading process. This often comes into play when filtering on the fulfillment of checklist items which are required for reading (such as in application status rules as well as, occasionally, bin movement rules). In these instances, the Checklist Items Required For Reading Status filter can be useful: