Windows operating system create lot of temporary files while usage. Prefetch files are one set of temporary files that help in better and faster loading of Windows and other program installed on it. Every time you open a program, the loading information is stored in set of prefetch files. These files are used for quicker loading of same program next time, without computer having to reference original source.
Prefetch files act as intermediate for providing loading information for faster and optimized loading of software on the computer. Over a period of time, prefetch cache can become stale and cause problems like slow system or freezing. In such case, you can open prefetch folder & delete pretch files and allow operating system create new set of prefetch files as you use the computer.
To summarize, prefetch files are good for your computer as it speed up the process of opening program applications. However, it is recommended to delete them once in a week or fortnight to make sure prefetch contents are updated and relevant as per current computer state.