This feature allows you to create an advanced layout from the active window on the current screen. The advanced layout will be named after the active app, and will have the dimensions of the active window and the position of the window on the current screen. It should be noted that applying an advanced layout on a screen with different dimensions can give different results (depending on the advanced layout configuration). When you create the layout from the current window the preferences are opened and the new layout is selected so that you can customise it, for example changing the name or making the window centred instead of anchored to the screen edges.
This feature can be helpful for example for people who use an app for screen casting and want to position a window with an exact size and position to ensure they capture the correct portion of the screen with their screen casting software.