Now that the desktop regains supremacy, Microsoft needed to add some serious innovations to its traditional user interface. Sometimes you can't have more than one monitor (like on a laptop), and some apps are simply better off maximized than they are snapped (such as Photoshop). Hence, the introduction of a longstanding feature of Linux and OS X: virtual desktops.
In this UI paradigm, the user has several desktops which they can organize as they see fit, and switch between them at will. With the Windows 10 virtual desktop system, it’s pretty easy to create desktops and close apps wherever they are via a redesigned Task Switcher (former Alt+Tab) which is now incorporated into the Desktop Switcher.
Unfortunately, moving apps between desktops is an unwieldy right-click affair, and repositioning desktops appears to be impossible in the Technical Preview. If OS X’s Mission Control, or even some of the Linux solutions are the benchmark, Microsoft still has a ways to go with its virtual desktop implementation.