Today user has no possibility to make settings how he want to be informed about todo. If the user is a manager and want to see what the team are doing he need to see a daily e-mail with all todo done/changed etc. The best if this todo will be incorporated into the daily features email (great Aha feature and your work here!).
Today when there is five persons assigned to a ToDo, user who reported the task will get several emails e.q. one of the user finished the Todo, somebody make a comment, etc. User working on this task need it. Managers just need to see what is going on on daily basis.
It would be great if there would be additional options to control to-do notifications. For example, to completely disable overdue to-do email notifications.