Not a dumb thought, but the answer is animation; things usually don't change much from one frame to the next, so most of the cache is still good. I think I read that Poser 8 actually does save and update it when doing animation.

Also, the render I currently have underway is the other way around. It has a lot of explicitly reflective detail and was a bear even without IDL in Poser 7.

Restarts would be great for those occasions when, after an hour or so, I'd really like to do something else for a while and resume the first render to run overnight.

Whichway