|It depends on who you ask. Probably depends on what you are trying to do.|
As I understand Prefetch, it's intent is to speed things up, but like other things in Windows, it is reported to possess the strange power of slowing things down.
I've heard advice both ways and have chosen to leave it alone because it rebuilds the content over time. Meaning that you might get short term results only.
Present your question on google search & see what you come up with. I checked mine just now, content approx 2.58mb, hardly worth thinking about.
Info at link below. Different slant than I've seen before. Modifying it seems mor reasonable than deleting it's contents.
There is nothing to learn from someone who already agrees with you.
Ccleaner seems to do a good job with some of the others with less hassle