Speaking about the notifications channel feature, Google will allow users to customize what they want to see in the notification shade. For example, you can limit the OS to display a notification when a screenshot is captured.
And now, Google announces a new feature to the developers called 'notification timeout,' which essentially allows developers to push a self-destructive notification. For instance, in India, we love shopping, and there are numerous portals to shop from, and the major one is Myntra. These days, Myntra run several discount offers, and they push notifications for the same now and then.
Myntra pushes a notification, and you open the app after few hours due to your busy schedule, and by the time you open the app, the offer is long gone. With this self-destructive notification feature, developers can choose a certain time for killing the notifications, and after that time, notifications will be destroyed automatically.
Nevertheless, this feature will be very much useful for the developers out there.