When Google launched the notification center in Chrome a couple of years ago, it gave users a way to see their notifications from Google+ and other Chrome apps/extensions which supported push notifications. There are undoubtedly some users who interact with this on a daily or at least frequent basis, but according to Google in a Chromium blog post this morning, very few people were actually visiting the notification center which has led the team to make the decision to discontinue it in an upcoming Chrome release. Once that happens, the dedicated notification center in Chrome for Windows, Mac, and Linux machines will be removed, but will remain for Chrome OS.
The idea behind the notification center was to allow users a way to see the notifications they may have missed due to being away from the computer when they came through. If something required a user to step away from the screen whether it was to go about something else in their day or to do just a couple of other tasks, one could simply open the notification center and check anything that came in. With little use of this feature on a consistent basis Google finds no reason to keep it around, and have stated that the decision to remove it is part of the process to streamline notifications for everyone.
In light of these upcoming changes, developers who have set up their apps or extensions to send out notifications to the notification center will likely want to adjust things, as Google mentions that notifications that go to the center will result in an error, and that "API events tied to the center will no longer fire." Google doesn't explicitly state when the changes will take place, so there's no hard date for when to expect the notification center to disappear. Having said that, developers would be wise to go about things swiftly. If you previous or currently use the notification center actively, Google likely has plans to introduce a new way of interacting with notifications on the desktop, so users probably won't be left without a way to see them altogether.