I've never seen indexing crunch, kept it on since the install.
Superfetch only does it for (the crunching/ hdd seeking), first minute after bootup or after shutting down a game but the pc is still fast while it's doing it. It would only be very stupid to turn it off unless you don't do anything with your pc except to browse new uncached pages all the time, as it very much boosts windows speed.
Or do you mean XP's prefetch? I have no idea.
Oh and the automatic defragger does it when my screen turns off ( after bout 2 hours of no activity) even if I turn off automatic defragging lol ( unless dfrg.exe or something like that is owt else, but it's that app according to the resource browser after I come back to my pc that causes the crunching)