I've used this to speed-up CLI commands which have a slow startup phase. I run the process up to the point where it finishes initializing things and starts reading input, SIGSTOP there, and resume it later. You can identify that "reading input" library call with strace, and intercept it dynamically with an LD_PRELOAD shim.

I haven't yet figured out how to (neatly) persist this to disk, so I just sort of make a mini server-loop that catches signals and dispatches a fork() for each one, and that's my fast version of the CLI command. Delightfully ugly :)

(The killer app I'm trying to apply this to is LaTeX, so that I can write math notes in Emacs, incrementally, without visible latency. Unfortunately the running LaTeX process is slightly convoluted, and needs a few more tricks to get working in this way. This trick works on the plain TeX command out-of-the-box (it's like a 50x speedup), so I think I'm on the right track...)