This isn't specific to Emacs; TeX is another notable example. Generally, this was a popular technique to dramatically improve start-up time on DEC PDP-10 and -2

This isn't specific to Emacs; TeX is another notable example. Generally, this was a popular technique to dramatically improve start-up time on DEC PDP-10 and -20 machines. There was support from the OS as well as the language runtimes to make it work (for instance, saving an image of a running program that had fd's open would still have to know they weren't open by the time the saved image was restarted).