As you know Windows 8 apps aren’t anything like traditional apps, one of the interesting feature about these apps is that even though they don’t have a close button, they do have a number of ways in which you can close them.
Yes, it is fun (at least to me) to drag down an app to close, but how about restarting a modern app? Most users will just close the app in anyway they know and then from the Start screen, they will just find and click the corresponding tile to launch. But in Windows 8.1 there is a quicker and easier way to restart apps without having to go back to the Start screen or even leaving the current screen for that matter.
If you want to try this, here is what you have to do: Open any Windows 8.1 app, drag it down, hold until you see the tile twist, then don’t let go and drag the app back-up and release, and the app will immediately restart, that simple. So now my best guess, this is the reason why Microsoft added the extra hold to close gesture, which I think is pretty useful.
In case you want to check an app really restarts, open the Task Manager, go to the Start screen, launch the Mail app, use the instructions I just mentioned, wait until Mail is fully started again, and switch quickly to the desktop, and you may just catch the Mail process going away and magically reappearing.