The prefetch folder is a software cache where Windows stores a lot of operations data. When Windows runs a process(Even boot processes.) the processor goes through many complicated calculations and sub-processes in order to get your process or program running. Windows saves some of that work in the prefetch folder for future reference, should it be needed at a later time, such as if you run the same process or program again. If you do then Windows consults the prefetch folder in order to avoid having to process all those calculations and sub-processes again, with the result that the system is a little faster having saved the use of the extra CPU cycles.

Some websites claim that if you regularly empty your prefetch folder it’ll speed up your machine: This couldn’t be further from the truth. (Linked page is over 3 years old but nevertheless relevant.) If you do so then Windows has to do all those calculations again, run all those .DLLs and sub-processes again, thus using up many extra CPU cycles and causing your computer to run slower: Windows will have no pre-processed information to consult, and therefore will have to compute the whole lot all over again.

"OK I see what you’re saying. Exactly how much information does Windows actually store in the prefetch folder?"

At most Windows stores calculation information for the last 128 recent processes. Files stored for prefetch have the suffix .pf. Delete that lot and Windows may end up having to do 128 sets of complicated calculations all over again: Your CPU won’t exactly be happy with you after having to process all those algorithms again unnecessarily – And your computer will work slower as a result.

Leave prefetch alone: It’s there for a reason, and removing part or all of it will not be beneficial to you or your computer.