I use spaces heavily and I have my windows arranged in a particular order. If I restart every application will be launched in the same space with many empty spaces.
If I unplug my external monitor, instead of adding those spaces to the others, the windows in them get resized and dumped into the macbook screen. They may or may not go back at funny sizes when the monitor is plugged back in.
I'd like to keep windows in specific spaces regardless of what else is going on.