Most comments are missing a major point. The app window is not being dragged to the side of your desktop. It is being put into a new temporary screen which can be shared with another document window. It does not snap to the side of the desktop. There are no icons, dock, menus or other desktop items. This is a perfect way to implement a small project window in which you want to use two documents. After you are fiished, just click the green dot and the temporary screen goes away and you are returned to your desktop. You can move freely between the temporary screen and permenant desktops that you have set up previously. It just sits there waiting for you to return.
One other thing. You can just drag a doc window to the screen top to put it in its own temporary workspace.
And last, the items in the temp files are named when you check your spaces. For example "Pages and Finder"