It would be nice if you could connect flowto your SharePoint calendar or create an app that worked with the SharePoint calendar. It would also be very helpful if you could create reservations like you could in the old SharePoint calendar which would allow users to make a reservation system for conference rooms, labs, or other resources that are shared within a company. Currently I use a workaround but I think it should be available again natively in sharepoint.
Instances where this would be helpful:
Schools or companies that share facilities, computer labs, or equipment that would like to have internal reservations that cannot be double booked.
Creating an app that allows employees to reserve something on the calendar and then uses flow to notify personnel who do not have to attend the meeting but do have to set up chairs or other equipment.