Admins can bulk delete tasks on any work order.
Sub-admins can do this for any work order with a service category and department that they have access to as long as they have been granted access to manage work orders and have NOT been restricted to certain service categories.
Regular users can do this for any work order that has been assigned to them or they have assigned to themselves (assuming they have been granted access to self assign work orders). Users will only be able to be assigned work orders that have the same service category on the work order that they have access to under their user permissions.
Within any work order with tasks, users have the option to delete one or multiple tasks. You can do so by going to the Task tab on a work order, checking multiple tasks and then clicking "Delete All Selected" as shown below.