The Dashboard function was introduced 10 years ago as a new feature in Mac OS X Tiger, and in that time there have been many introductions for it widgetov. Some could also be downloaded from the official website Applol, well that was it temporarily disabled 2 years ago and that was the first indication that Dashboard was slowly ending. The site has since been turned back on, but Apple since then he has not paid any attention to the Dashboard, quite the contrary. Instead of new ones widgetov for Dashboard Apple enriched the notification center with the support of its own widgetov, which are a kind of miniadd-on for existing applications from Mac App Store or for system applications.
Now there was another, third indication that Apple may remove the service after ten years, to which a separate screen to the left of the desktop is dedicated. It was noticed by users released yesterday beta OS X El Capitan Developer version Preview 7, where the function is disabled by default and must be activated in the system settings by checking the "As Space" option in the Dashboard section. On the other hand, the function was also disabled in OS X Yosemite, but only minimum users noticed that the function would be missing, since for most users the function was already active after switching from OS X Mavericks.
So that's quite logical. Widgety in the notification center are within the convergence iOS and OSX. Dashboard was more "Android-like"
What seems more useless to me is the Launch something screen...