Or prevent law enforcement, or other "overseers" from believing you visited a page.
I can see children getting punkd by drive-by prefetch and reporting to teaching staff that X visited a neo-nazi site or, Y downloaded porn during class, etc..
"Prefetch did it" is probably not going to be apparent to most, and is going to sound like a weaksauce excuse.
On the other hand if you're visiting pages that link to neo-nazi content or pornography just one link away from the page you're currently on, chances are the page you're currently on would violate whatever acceptable use policy you're supposed to be following.
Unless whoever is patrolling this filtering is completely insane just show them that page that you were on and how hovering over the link triggers the filter.
Every instance of web filtering I've been subject to in my life just blocks the bad page and the admins expect people to have a few bad requests just by accident or whatever. You'd have to be constantly hitting the filter for it to actually become a real issue.
I can see children getting punkd by drive-by prefetch and reporting to teaching staff that X visited a neo-nazi site or, Y downloaded porn during class, etc..
"Prefetch did it" is probably not going to be apparent to most, and is going to sound like a weaksauce excuse.