Ratpoison hardly nullifies the need for a second monitor. It's all about screen real estate. You're working on a tough programming problem, you want a few different files of code, a browser open to some documentation, and some extra emacs (in my case) buffers and/or terminals for various errands. You just want it all to be visible at once. It's much easier to just keep everything there rather than "put it away" somewhere that's not visible. This is true regardless of your window manager.
