Window snapping in macOS Sierra
Mac users now have a window snapping feature built directly into macOS Sierra, which allows users to easily snap windows to aspects of the screen or against one another. This offers a nice way to quickly and precisely align windows, and it's more or less the Mac equivalent feature of window snapping from the Microsoft Windows world.
Window snapping on the Mac will snap windows to any of the following targets: edges of other windows, the menu bar, the top of the Dock (if visible), and the sides of the screen.
With several windows open on the Mac display, grab one and drag it against a snap target. You'll "feel" the dragged window snap to place, repeat with additional windows as desired
The window snapping ability in macOS is a bit more full featured than what is offered in the Windows world, with a broader range of snap targets. You can snap however many windows together that you can fit on screen, regardless of their size.
While you can't completely turn off window snapping, you can temporarily disable window snapping in macOS with a keystroke action when moving windows around on the screen. To temporarily disable window snapping, hold down the Option (alt) key when you're dragging and moving windows around.