We’ve already described macOS Sierra’s new window-snapping feature but we didn’t realize Sierra also introduces a new feature that lets you ultra-quickly expand windows to the edge of the screen.
Using the feature is simple. Just hover the mouse cursor over the edge of a window until it turns into some kind of arrow cursor, and then double-click. The window will expand in the direction the arrow was pointing.
See the animated GIF below for an example.
UPDATE: Matthias Gansrigler points out that holding down the Option (Alt) key while performing the double-click causes the window to expand in both directions. Give it a try to see what he means!