We had following use-case (problem): We want to disable notifications that are sent out to students, when submitted a solution to the assign (mod_assign) activity.
Our approach was to solve it over the given assign settings, e.g. set "sendstudentnotifications" to "No". But even it was disabled in the activity, Moodle sends out the notification to the students.
After investigating, I've found out, that it's because of the global "notification preferences". If the student X has under the "Assignment notifications in "Email" the settings on "On", he will get notifications. It doesn't matter, if the activity Y has it disabled or not.
For my understanding, the activity setting should overrule the global "notification preferences". It could be, that the student wants to receive assignment notifications. But in course Z the teacher don't want it (doesn't matter why!) and configures it correctly in the activity. But in the end it's not working, as the teacher expected.
Did you have the same problems? Or have we missed something? Maybe we should create a Moodle Tracker issue for this, if more people are affected.