-no map has to do with OFPs memory handling system. If you add nomap to the startup process or modfolder you save memory, but may lose some performance during game play. At least that's what I'm told. I'm no expert and never delved to deeply into the problem.
I use -nomap myself, because it prevents my computer from crashing/freezing when I play on big maps like the Tonali islands. But it has nothing to do with mission editing.
Computer related topics like these are best answered on the official forums:
www.flashpoint1985.com