It has been posible to turn on or off certain Windows features for a long time and if you don't need a particular component, then why should you bother loading it every time you start Windows?
An example of this is Windows Tablet PC Options Components that get installed into Windows Vista and 7 (but not in 8). It gets installed on your PC by default, even if you don't have a tablet PC. It seems a pointless exercise for most people. Fortunately, you can remove it.
To add or remove Windows Vista, 7 and 8 components, go to the Control Panel (press Windows+X on Windows 8 PCs) and then open Programs and Features. Click the link in the panel on the left labelled Turn Windows features on or off. After a few seconds of disk activity you will see a list of Windows components and tick boxes next to them to enable or disable them.
Each version of Windows is slightly different. Windows Vista and 7 are quite similar, but 8 is a radically new version of the operating system and it has a different range of options. Some items are similar though and there is an option to turn off Internet Explorer for example. This could be used if you only ever run Firefox or Chrome. There is also Windows Fax and Scan, which is useful if you fax and scan from within Windows, but not everyone does. Items you probably don't want in Windows Vista and 7 include the unnecessary tablet PC components.
At one time there wasn't a simple way of removing Windows components like Internet Explorer, so it's good to know it can be done quite easily these days. Whether it is completely removed or just hidden is hard to say, but at least the option to remove it is there and it will be welcomed by those people that really don't like Microsoft's web browser.
Other features that can be removed include Media Features. This is a category containing Windows DVD Maker, Windows Media Center and Windows Media Player. Each can be disabled separately.
Check out the Print and Document Services for items that you don't need.
Windows gadget Platform can be turned on or off in Vista and 7. This is the component that enables you to put gadgets on the desktop. (The Sidebar is required in Vista, but not in Windows 7, and 8 doesn't support desktop gadgets).
Windows Search can be turned on or off, plus a few other miscellaneous components.