It won't hurt anything if you check it, but I wouldn't bother.
Your computer will automatically replace anything that's needed. Prefetch amounts to what your computer thinks you're going to use next.
Here's what Microsoft says about ithttp://windows.microsoft.com/en-us/windows-vista/what-is-the-prefetch-folder
And here's what the Wiki sayshttp://en.wikipedia.org/wiki/Prefetcher
So it may help speed startup, but isn't critical.