Human beings do not always live with great changes and characteristics and sometimes they are those little things that without realizing it make it easier for us to do a task that a priori we do not usually pay attention to, and that is precisely the percentage of battery remaining in our wireless devices.
Among them, the most important we could say would be the keyboard since it is the main means of moving around the computer and entering information, that is, you can live without a mouse or trackpad but not without a keyboard and that is where this little notification comes in.
Before this option was available as such, in previous versions of the operating system simply the bluetooth icon was blinking to make you see that something was wrong, on the contrary it was not clear enough so that if you were working focused on a program with a project it would attract your attention enough to realize it.
Supposedly all this has been taken into account in Cupertino to give the importance it deserves to a notice like this, something that I like and I think it is a total and absolute success. Apart from this detail, as you already know, in this new version of the operating system programs such as FaceTime, iMessage and many other features are also integrated directly from the notification center, which is a considerable improvement.
Something that we must take into account is that Apple is starting to give more and more importance to said notification center, seeing that many of the daily tasks can be grouped in more centralized areas of the system and not just as individualized programs.
More information - OS X Mavericks and the new Mission Control option with the Dashboard
Source - iClarified