I was curious so I ran a little test. I set my system ahead 14 days, and ran the analyze button in CCleaner. Seems CCleaner will clean anything in the prefetch if it has not been accessed in 14 days, including items you routinely use. (see screeny) The items I show only appear after setting my system ahead. So if you are on vacation for a few weeks, come back and run CCleaner, it will most likely empty your entire prefetch folder.
Tipton