For web apps I can imagine good uses for notifications, like how I have a Google Calendar tab pinned and it's useful for it to be able to alert me that I have a meeting in 15 minutes.
I wish we could time limit notifications, like it'd be nice to allow notifications to an app for a fixed time period (say a barber queueing app) but I dont want to see ads served by them outside of that time period.
Seems like you don't need an ML system here, just an expert system, which is just, always reject.