Sometimes when you have left the screen on, and you walked away for a short while, like:
- Using the washroom
- Getting a slice of cake / snacks from a friendly colleague
- Opening the door for someone in need
Then you may miss a notification from some Apps.
While the notification showing duration should be possible to be modified, that is not too reliable.
Instead, I'll use "alert" for notifications to ensure they stays until I dismiss them.