Many users are accustomed that in text editor exist ability to split window and see two part of one document on one window. They will be astonished that Writer has no Split Window.
It would be excellent, if in Writer would be ability to Split Window, like in Calc.
It is useful to split window horizontally and vertically. But not because users need four parts of document at once. But because on classical monitors it is more handy to place parts of window top-bottom, and on widescreen monitors more comfortable to arrange left-right.
This ability may significantly improve productivity because it reduces amount of open windows, especially if users hold similar documents in one file. Exists other tasks, when it will be more comfortable with split-ed window.
At this moment exist ability to create new window, but it is useful for other tasks, than split window.