When you evidently created Tasks from a Checklist or the Tasks are no longer applicable, you can delete them in bulk rather than individually.

When you click on the Delete button in the Checklist Instance

Delete Checklist Instance

You have the choice to 

  • delete all open (remaining tasks)
  • delete all tasks (also already closed ones)

Note that this functionality is available for Checklist Administrators only.

Delete Checklist Instances and Tasks

You navigate to the Checklist Instance from the Checklist (related list) or from the Checklist Instance component:

Checklist Instance comonent