As far as I know I believe this is useful when you are running a layout for mala that is set for lo rez probably when using an arcade monitor. A layout that is fixed is retro GUI wich can be found on the mala website. if youre running mala under a monitor that doesnt support the resolution of the fixed layout this option can be used to force the layout to the proper resolution. I am not 100 percent sure of this as i am new to mala and myself trying to get everything figured out but i hope that this helps a little.