The ability to easily snap two desktop windows side-by-side was introduced originally on Windows 7 as Aero Snap. Users can drag any window to the edges of the screen, and the window would expand to fill the screen or take up height of the screen. Windows 8 refined the feature for Modern UI apps, allowing two apps to run side-by-side simultaneously.
While the ability to snap two windows side-by-side with Windows 7's Aero Snap was useful, Microsoft is taking this a step further with Snap Assist on Windows 10.
This makes it more efficient to choose which app to snap into the second window, and Microsoft found that 90% of Windows Insiders choose an app to snap in the second window from the recently used windows list.
Snap fill allows you to easily snap windows into configurable sizes. The feature is similar to Aero Snap, but rather than automatically snapping two windows together that each occupy 50% of your screen space, Snap Fill allows you to allocate a larger portion of your screen to one app and then fill the remaining portion of your screen with a second app.
For enterprise users who use multiple displays or for those with hybrids and two-in-one notebooks, Microsoft is also making Snap easier.
Windows 10 allows multi-monitor users to snap to a corner or edge shared by both displays, a feature that was previously not possible with earlier versions of Windows. Snap Assist will let you see all the windows across all displays so you can snap different screens together more easily without having to drag the windows across your displays.
For hybrid owners, Snap works seamlessly with Continuum, allowing you to preserve your Snaps when you switch between notebook and tablet modes. As Store apps are now opened in resizable windows alongside traditional desktop apps, Windows 10 allows users to snap both types of apps together.