We often find with new tracking releases previous tracking implementation can break. I use calendar events to mark the occassion but don't always need it on every report.
Example, we implemented some custom ad tracking and it dropped most of our custom events by 8% (but not all of our events). In turn, it dropped many of our calculated metrics and custom segments. I used calendar events to mark the period but I don't want this on all the reports, I only want to show the calendar event on reports where the events and calcualted metrics are used. It's cluttering many of my dashboards.
We have put the notice under our company notices but no one reads those. The calendar events are more effective to prevent people from using metrics that were incorrect for a period of time.
Would also be good to have a similar alert system in Discover