Note You must have Delete permission for a Collection security object to delete that collection.
If you selected a subcollection, you can delete only its association from the parent collection, or all instances of that collection.
Deleting a collection removes it completely from the SMS site database. The deletion includes any instances of the collection that were subcollections of another collection.
When you delete a collection, its resources remain in the SMS site database. However, SMS deletes any advertisements that specified the collection.
Delete All Resources in a Collection
Using Collections to Manage Resources Overview