There are 3 different statuses which your Tasks can be set to:
For planning ahead, to give another admin a chance to check content or to pause a task temporarily. This state is perfect for creating and assigning tasks that aren’t quite ready for teams to use.
Tasks that are currently relevant to teams and ready to action on the Complete Tasks page.
Tasks aren't in action anymore - the task's history is saved but tasks are tidied away and can be recalled upon down the line. They will show in their own Archived section at the bottom of your Manage Tasks page.
Changing a published task to draft
Set a Published task to Draft in order to remove it from your teams' Complete Tasks page
Simply click into the task's editor and hit Unpublish
Once you're ready, you can Publish this task again at any time
Ad hoc tasks that are Draft will not appear in the Add Task list on teams' Complete Tasks page
Draft tasks will never show on your teams' Complete Tasks page, whether they're assigned to Sites or not
Archiving a task
Set any unwanted task as Archived to tidy up your Manage Tasks page
Simply click into the task's editor and hit More > then Archive
It will now show in the Archived section at the bottom of your Manage Tasks page
If you ever want to return to this task, you can Publish it again at any time via the task editor
Archived tasks will never show on your teams' Complete Tasks page, whether they're assigned to Sites or not
Archiving tasks in bulk
Simply head to your Manage Tasks page and click the check box beside your unwanted task(s)
Then click the archive button at the top of the page
Deleting a task
There's also the option to delete the task completely. Use with caution - deleting tasks will mean they're removed from all sites and your Manage Tasks page forever!
Simply head to your Manage Tasks page and scroll to the bottom section where all your Archived Tasks are. Click your unwanted task and hit edit > more > delete.