I want to use it when for some reason I don't have a save file (I do that a lot because I install everything with makesb) and I create one just to save some settings on my profile. Like I just installed my web browser using makesb name_of_the_browser and I want to save my preferences so that they are persistent between reboots.
For that I create a save file changes.fs4 and I want it to receive the changes rightaway because right after that I want to run a makesb -f changes.fs4 so that my changes are saved in a module.
You see, if I don't use save-session I will have to reboot in order to have my preferences saved on the changes.fs4. Alpha boots in less than 30 seconds but it's still a tedious process