I use a lot of raster effects in my work. A lot. I can easily have several thousand paths with effects on them. (Mostly Gaussian Blur, thanks for speeding that one up a few versions ago!)

Some experimentation with saving multiple copies of an effect-heavy file with different raster effects resolutions confirmed my suspicion that the file size varies greatly with the effect PPI:

300ppi: 70.8MB
150ppi: 28.8MB
72ppi: 14.4MB
2ppi: 5.4MB

Reloading the 300ppi copy made it obvious that there's a cache of raster effects in the file, as I didn't have to wait through a half a minute of progress bars while AI rendered a few thousand gaussian blurs like I did a little earlier when I bumped the resolution up.

I would love to be able to reclaim a ton of disc space by saving my files without all these images. I am perfectly happy to accept the tradeoff of it taking a moment to render them all when I load in a file.

I envision another checkbox in the Save dialogue, probably right under the 'PDF compatibility' checkbox. "Include raster effect cache"? Defaults to on for new documents, will come up as off if I do a Save As on a file that I've already saved with it off, just like all the other checkboxes in there.