I believe they should exist (for all items) if turning them off isn't going to be a group setting, with a default of off.  I'd also like to see it set so that someone can't send multiple notifications (of the same type?) within a short time if they can't be turned off.  (A recent reason for this is the Upload Directory where a notification is sent for each file uploaded.  In a test, that resulted in over 100 notifications!)