The concept comes from designer Bill Labus who says that he finds "double-clicking the home button to be irritating" when trying to access the multitasking menu for iOS, so he has come up with an elegantly simple solution to fix that issue - he has merged the multitasking menu with the Control Center. This means that instead of double-tapping the home button, you simply swipe up from the bottom of the display to pull up a unified screen that holds both the Control Center on the bottom and your list of open apps on top.
It certainly seems like a faster option, and gesture controls are usually more user-friendly than buttons that work double (or triple) duty, like the iOS home button does now. As it stands, if you tap the home button, you get to your home screen; holding the home button brings up Siri (on compatible devices); and, double-tapping brings up the multitasking menu. Apple tends to prefer simplicity, so Labus' design makes more sense from that standpoint. We approve!