Many VPO modules (like RFIs, Submittals, and Action Items) use a field called "ball-in-court" to assign a user to a specific item. When a user's name (or email) is entered in the ball-in-court field, that user will receive an email notifying them that they've been assigned. The idea behind the ball-in-court field is to use it to pass an item on to another person.
The ball-in-court notifications work the same way on all modules. You will only receive a notification if the ball-in-court has been changed from something else (another person or a blank) to you.
Here are some examples:
If you are working on a Submittal where the ball-in-court had your name in it when you opened it, and you made some changes to other fields, and your name was still in the ball-in-court field when you saved and exited, you will not receive a notification.
If a user opens a Submittal to work on it where it had their name in the ball-in-court when they opened it, and then the user changed the ball-in-court to you, and saved and exited - you will receive a notification. The ball-in-court changed and that Submittal has now been assigned to you.