The Benefits of a Clean Installation
What is a clean installation? And what are the benefits?
A clean installation is when you erase all existent files and reinstall the whole system. This way you get rid of the junk in your hard drive and also eliminate some hidden programs that could be slowing your computer. If you need to keep your files, you can back up them. After the clean installation, only the essential is on your computer, which will be running faster and safer, and you can install any additional applications you need. I recommend a clean installation if your computer is very slow.
If you want to know more about it, here is an excellent article to read on Lifehacker: In Defense of the Clean Install.