I think they mean tearing an editor (or other panel) out into another window to move to their other monitor.
Currently you can open another window, but it comes with its own explorer, terminal, problems, test runner, etc. Soon you'll have the same file opened twice in different screens, and... bleh.
But you can just drag it across two screens and divide it up along the border? From my experience that works fine as long as your screens have the same resolution.
True, you can divide the editor into two (or more) splits, and also divide the bottom part (Terminal/Debug Console/Problems). If you're the type that doesn't move windows around often, that could work.
Currently you can open another window, but it comes with its own explorer, terminal, problems, test runner, etc. Soon you'll have the same file opened twice in different screens, and... bleh.