The reason is that every operating system, including Windows, is a sort of ecosystem in it and is subject to constant changes. Programs are installed and de-installed, settings are changed, updates added, older applications are simply forgotten, contents are downloaded and many more. Each modification leaves its traces and all together they make the system slower and less capable. What is more, Windows as such is not adjusted to your special demands and is installed with default settings that serve Microsoft more than you.

A new installation hardly solves the one problem and is not solution at all for the other. It is time-consuming and with all the program settings, upgrades, service packs and security updates required it easily takes a whole weekend but is hardly effective when it comes to unnecessarily started services.

Yet, there is a considerably faster method which in addition prevents other signs of wear: SuperEasy SpeedUp.